Fabtech K1223DL 1.5-Inch Dirt Logic UCA Lift Kit — 2025 Silverado Trail Boss / Sierra AT4 4WD V8 Gas

Fabtech K1223DL specifies front Dirt Logic 2.5 reservoir coilovers, replacement upper control arms, rear block hardware and two rear Dirt Logic 2.25 non-reservoir shocks for factory Trail Boss/AT4 trucks.

Application

• 2025 Chevrolet Silverado 1500 Custom Trail Boss or LT Trail Boss, or GMC Sierra 1500 AT4; V8 gasoline, 4WD, with the specified factory suspension. Verify exact vehicle equipment and rear axle/leaf-spring configuration before ordering.
• Nominal 1.5-inch increase for the factory Trail Boss/AT4 application. Does not fit diesel, four-cylinder, Adaptive Ride Control, Super Cruise or standard-cab configurations. OEM wheels and tires cannot be used.
• 2026 models and ordinary Silverado/Sierra trims are outside this listing. The supplied round U-bolts must match the actual application.

Package contents

• One FTS21309 component box: driver and passenger upper control arms, TWO ball joints, TWO FTBK15 1.5-inch rear blocks, FOUR FT768U round U-bolts and specified bushings, sleeves, arm spacers and hardware. No front shock spacers are supplied in this box.
• One FTS21257 gasoline FRONT reservoir-coilover PAIR: one driver FT820632D and one passenger FT820632P, TWO reservoir mounts and specified mounting hardware/clamps. This replaces the factory front coilovers.
• TWO FTS811452 REAR Dirt Logic 2.25 NON-reservoir shocks. FOUR new dampers total. The rear shocks differ from the reservoir front assemblies.

Installation and requirements

• Professional installation required. Read FT21268i, FT820632i and FT811452i and inspect the complete kit and factory alignment before work. Use the Dirt Logic branch and its specific hardware.
• The arm installation requires cutting the factory frame bumpstop tabs and fitting the specified greased bushings, sleeves, ball joints and arm spacers.
• The front-coilover instructions require opening the upper mounting hole 1/2 inch away from the CV axle with a barrel sander, mounting the coilover offset away from the axle, and drilling TWO 1/4-inch reservoir-mount holes per side for the supplied self-tapping bolts and clamps. Do not remove the pressurized reservoir hoses or coil preload.
• Install the correct rear blocks and round U-bolts and the selected non-reservoir rear shocks with their specified bushing kits. Do not substitute other shock numbers from generic system examples or infer added rear height from the block dimension alone.
• Check brake-hose, ABS-wire and wheel/tire clearances, align to factory specifications, adjust headlights and recheck fasteners after 50 miles and periodically.

Tire and wheel guidance

• Manufacturer guidance, with minor trimming and 5-inch wheel backspacing: 33/12.50R20 on 20×9 wheels or 285/55R22 on 22×9 wheels. Verify actual clearance. Wheels and tires are sold separately.

Manufacturer part number: K1223DL. Manufacturer product details.

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