Fitment Pilot
Garage Saved garage
Menu

ReadyLIFT 66-3921 1.75 inch GM AT4 and Trail Boss leveling kit

Is the ReadyLIFT 66-3921 1.75 inch GM AT4 and Trail Boss leveling kit the leveling kits pick here, or just one of three?

Best fit for Silverado Trail Boss and Sierra AT4 shoppers who need a leveling kit designed around factory-lift geometry.

Put it next to the Rough Country leveling and lift kit and the ReadyLIFT SST leveling and lift kit and the ReadyLIFT 66-3921 1.75 inch GM AT4 and Trail Boss leveling kit leads for one kind of buyer while giving ground elsewhere. None of the three is the automatic answer, so read the package, fitment, and install rows before you read the price.

Nicole, Fitment Pilot editor

Reviewed by Nicole

Fitment

2019-2026 Silverado 1500 Trail Boss, excluding ZR2

Verify first

Use on Silverado 1500 Trail Boss factory-lift trucks when the current ReadyLIFT or seller fitment tool confirms the exact year, cab, drive, and trim. The product is not a normal-height Silverado spacer kit.

Part number
66-3921
Choose it when
Best fit for Silverado Trail Boss and Sierra AT4 shoppers who need a leveling kit designed around factory-lift geometry.
Pass when
It stops being the right call the moment this holds: Silverado ZR2
Our cross-product compare

Same category. Different reason to buy.

Evidence level B
Best for
A factory-lift GM 1500 leveling kit for Trail Boss and AT4 trucks that need control-arm and strut-spacer geometry built around the OEM 2 inch lift.
A broad Rough Country suspension family for truck owners comparing front levels, loaded struts, and mild lift kits after exact trim and suspension-package checks.
A ReadyLIFT SST family for shoppers who want vehicle-specific spacer, control-arm, or mild lift packages with official application and warranty checks.
What's included
Front lift: 1.75 inches · Install type: Top and bottom strut spacers with tubular upper control arms
Coverage type: Truck lift-kit product family
Exact contents depend on the SST leveling and lift kit SKU you select for your truck.
Product approach
Do not substitute normal-height GM 1500 spacer or loaded-strut products on Trail Boss/AT4 routes without exact product confirmation.
Prefer Walmart and eBay when exact identity and seller terms are comparable.
Documented fitment only -- no standout approach beyond exact application is recorded for the SST leveling and lift kit.
Install burden
Moderate install. Exact 66-3921 SKU and UPC 804879610489
Moderate install. exact Rough Country SKU
Moderate install. exact ReadyLIFT SKU
Fitment
Confirm the exact ReadyLIFT 66-3921 1.75 inch GM AT4 and Trail Boss leveling kit application for Chevrolet Silverado 1500 Trail Boss factory-lift trucks before ordering.
Confirm the exact Rough Country leveling and lift kit application for Ram 1500 SLT Quad Cab 4x4 before ordering.
Confirm the exact ReadyLIFT SST leveling and lift kit application for Ram 1500 SLT Quad Cab 4x4 before ordering.
Choose it when
Pick the 66-3921 1.75 inch GM AT4 and Trail Boss leveling kit over the Rough Country leveling and lift kit and the ReadyLIFT SST leveling and lift kit when you want an OE-grade replacement with the widest dealer and parts-store availability.
Choose the leveling and lift kit when it is the exact match for your truck and the ReadyLIFT 66-3921 1.75 inch GM AT4 and Trail Boss leveling kit and the ReadyLIFT SST leveling and lift kit do not list your application.
Choose the SST leveling and lift kit when it is the exact match for your truck and the ReadyLIFT 66-3921 1.75 inch GM AT4 and Trail Boss leveling kit and the Rough Country leveling and lift kit do not list your application.
Current decision file

ReadyLIFT 66-3921 1.75 inch GM AT4 and Trail Boss leveling kit

Part 66-3921

Best for
A factory-lift GM 1500 leveling kit for Trail Boss and AT4 trucks that need control-arm and strut-spacer geometry built around the OEM 2 inch lift.
What's included
Front lift: 1.75 inches · Install type: Top and bottom strut spacers with tubular upper control arms
Product approach
Do not substitute normal-height GM 1500 spacer or loaded-strut products on Trail Boss/AT4 routes without exact product confirmation.
Install burden
Moderate install. Exact 66-3921 SKU and UPC 804879610489
Fitment
Confirm the exact ReadyLIFT 66-3921 1.75 inch GM AT4 and Trail Boss leveling kit application for Chevrolet Silverado 1500 Trail Boss factory-lift trucks before ordering.
Choose it when
Pick the 66-3921 1.75 inch GM AT4 and Trail Boss leveling kit over the Rough Country leveling and lift kit and the ReadyLIFT SST leveling and lift kit when you want an OE-grade replacement with the widest dealer and parts-store availability.
How we compared

Compared from exact part-number documents, documented fitment, included hardware, install notes, and current seller access. Retailer star ratings are not treated as proof of what owners think.

2in spacertubular UCAhardware x8
In the boxDrawn to explain, not a product photo.
Leveling kits owned fitment checklist visual
Visual unavailable
Illustration
Where to buy it

Seller offers

Each seller on its own terms - prices and stock reflect the date shown with each seller and can change; the seller's checkout price is final.

Paid link

Amazon

Worth a look when the exact part number is sold direct, but confirm the seller of record before you order.

Price, availability, seller details, ratings, and reviews are shown only on Amazon.

As an Amazon Associate I earn from qualifying purchases.

Available at Amazon

Other retailers to check

These other-retailer searches use the brand and part number shown on this page. We earn nothing if you buy through them.

Other retailer

Summit Racing

House fitment data and manufacturer spec sheets ride along on their pages, which makes it a good spot to sanity-check the part number.

Search with the brand and part number shown on this page, then confirm the manufacturer part number before ordering.

Search Summit Racing
Other retailer

Walmart

A broad marketplace where third-party sellers vary widely, so check who is actually selling and how returns work.

Search with the brand and part number shown on this page, then verify the exact seller, item condition, fitment, and return terms.

Search Walmart

Price checks build up as sellers are rechecked over time. The seller's checkout page has the final say; make sure stock, exact SKU, and seller details all agree before you order.

Report an issue
Direct retailer Amazon Check price and availability there As an Amazon Associate I earn from qualifying purchases.
Available at Amazon
Decision trail Check these before you buy.
Part ReadyLIFT 66-3921 1.75 inch GM AT4 and Trail Boss leveling kit Part 66-3921. ReadyLIFT resource available.
Fits 2019-2026 Chevrolet Silverado 1500 Trail Boss factory-lift trucks Use on Silverado 1500 Trail Boss factory-lift trucks when the current ReadyLIFT or seller fitment tool confirms the exact year, cab, drive, and trim. The product is not a normal-height Silverado spacer kit.
Watch for Leveling Kits checkout checks Confirm suspension package, air-suspension exclusions, alignment plan, tire clearance, brake-line routing, and warranty impact before checkout.
Other retailer · Seller 2 other retailer searches Search with the brand and part number shown here, then confirm the exact part and fitment with the retailer.
Photos Category visual The photo shows the category, not this exact part; an exact product photo appears once image rights are confirmed.
If unsure Compare, read, or report If the seller page, vehicle details, or photos do not line up, compare sellers, read the guide, or report the issue.
The evidence

Fitment and install resources

Reviewed 2026-06-25

Editorial method

What we checked on this page

We check the ReadyLIFT 66-3921 1.75 inch GM AT4 and Trail Boss leveling kit for exact part identity, seller options, stock and price dates, photo rights, and official resources. FitmentPilot combines automated vehicle database indexing with human automotive editorial review. Rather than presenting generic affiliate catalogs, our system evaluates the exact mechanical constraints of each chassis platform — from bolt circle geometry and motion ratios to factory package exclusions — giving truck owners complete confidence before checkout.

Sellers3 seller destinations

Paid offers and other retailer searches are labeled separately so you can choose where to check.

FreshnessConfirm stock at the retailer

Check current stock and price with the retailer before ordering.

PhotosCategory visual only

This photo shows the part category, not this exact product. Confirm SKU, size, and kit contents before ordering.

Resources2 official resources

Install, fitment, spec, or warranty resources are available before checkout.

An exact product photo appears here once image rights are confirmed.

Choose it, pass, or verify

A factory-lift GM 1500 leveling kit for Trail Boss and AT4 trucks that need control-arm and strut-spacer geometry built around the OEM 2 inch lift.

Choose it if

  • Best fit for Silverado Trail Boss and Sierra AT4 shoppers who need a leveling kit designed around factory-lift geometry.
  • Do not substitute normal-height GM 1500 spacer or loaded-strut products on Trail Boss/AT4 routes without exact product confirmation.
  • Compare Walmart, eBay, ReadyLIFT direct, and specialty sellers while refreshing seller stock, return terms, and exact SKU before checkout.
  • Use on Silverado 1500 Trail Boss factory-lift trucks when the current ReadyLIFT or seller fitment tool confirms the exact year, cab, drive, and trim. The product is not a normal-height Silverado spacer kit.

Pass if

  • The ReadyLIFT 66-3921 1.75 inch GM AT4 and Trail Boss leveling kit is not the right choice when your truck falls outside 2019-2026 Chevrolet Silverado 1500 Trail Boss factory-lift trucks, or its trim, engine, and package cannot be matched to the documented application.
  • Pass when this exclusion applies: Silverado ZR2
  • Choose another kit when the truck needs more height, rear-load support, adjustable damping, or hardware this package does not include.

Verify

  • Exact 66-3921 SKU and UPC 804879610489
  • Trail Boss trim and current seller fitment tool
  • Wheel/tire test fit, CV boot care, alignment, headlamp aim, ADAS calibration, and 500-mile recheck
  • The checked public route is a 2024 LT Trail Boss 4x4 Crew Cab. Custom Trail Boss, other cabs, older overlapping body styles, dealer-lift trucks, aftermarket lifts, and ZR2 need current seller and installer checks before inheriting this answer.
Workshop & DIY Guidelines

ReadyLIFT 66-3921 1.75 inch GM AT4 and Trail Boss leveling kit Installation & Fitment Protocol

Front leveling kits work by adding a top-mount or preload spacer above the factory coilover strut, neutralizing the built-in factory rake. Because independent front suspension operates on a motion ratio (typically ~1:1.5 to 1:2.0), the physical spacer thickness is smaller than the resulting ride height gain. A 1.25-inch thick spacer produces approximately 2.0 inches of net lift at the wheel hub.

Install Difficulty

Shop & Bench Specs

Difficulty: Moderate (3/5)

Estimated Install Time: 2.5 – 4.0 hours (DIY Garage) / 1.5 – 2.5 hours (Pro Shop)

Required Tools

Installation Equipment

  • Heavy-duty hydraulic floor jack (3-ton+) & matching safety jack stands
  • Calibrated torque wrench (50–250 lb-ft range)
  • Metric socket & combination wrench set (15mm, 18mm, 19mm, 21mm, 24mm)
  • Ball joint separator / tie rod puller tool (prevents boot tearing)
Post-Install Safety

Post-Install Protocol

  • Mandatory 4-wheel computer alignment within 50 miles of install to set toe and camber.
  • Re-torque all chassis fasteners, strut top nuts, lower control arm bolts, and wheel lug nuts at 50 and 500 miles.
  • Re-aim headlight vertical cutoffs downward to compensate for raised front nose height.

Wear Triggers & Maintenance Checks

  • Upper ball joint binding at full suspension droop if lift exceeds 2.25 inches without aftermarket control arms.
  • Accelerated inner tire edge wear if alignment toe-in is not corrected post-installation.
  • Front CV axle boot rib-rubbing and grease weeping under sustained 4WD high-speed operation.

Chassis Fitment Context

Direct-fit automotive parts are engineered around specific chassis mounting coordinates, suspension stroke limits, and load capacities. Ensuring compatibility requires cross-referencing vehicle year, trim, powertrain, and suspension package options.

Automotive platforms undergo major architectural overhauls approximately every 6 to 8 years, accompanied by mid-cycle refreshes every 3 to 4 years that often revise bumper valances, headlight housings, wiring harnesses, and suspension damping calibrations.

Pre-Installation Unboxing Verification Checklist

Step 01: Confirm Physical SKU & Labeling

Inspect outer box label against your order invoice and the manufacturer part number shown here before opening hardware bags.

Step 02: Dry-Fit & Hardware Inventory

Unpack fasteners, brackets, and instructions. Perform a preliminary dry-fit check against the vehicle before removing factory components.

Step 03: Review Torque & Thread Requirements

Identify critical torque values and whether thread locker (Blue Loctite) or anti-seize compound is required by the manufacturer.

Step 04: Plan Post-Install Calibration

For suspension, steering, or lighting parts, schedule a professional alignment and verify forward-facing ADAS sensor calibration.

Related guides