RetraxPRO XR Retractable Tonneau Cover with T-Slot Rails for 2014-2019 Chevrolet Silverado 1500/2500/3500 / GMC Sierra 1500/2500/3500 (8' Bed)

Here's the short version. Follow Retrax's install sheet (below) for your truck's exact steps, part letters and torque settings.

1. Assemble the cover. Remove the shipping screws, brackets and white shipping tubes from both sides, and keep one shipping bracket to use as a spacer later. Pull the cover 6-8" out of the canister and hold it there while you guide it into each side rail's channel and seat the rails in the canister. Fasten the rails to the canister with the four 10-32 x 7/16" screws, then slide the front cover under the rails and fasten it through the top of the rails with the two 10-24 x 3/4" screws and the 1/8" Allen wrench, all to 32 in-lb. Leave the protective film on until the end.
2. Set it on the bed. Some drop-in bed liners need notching at the front corners to clear the canister. With two people, lift the cover onto the bed with the canister at the bulkhead and the front seal lying flat on the bulkhead; trim the seal if it runs past the bed rail caps. Slide the cover back and use the shipping bracket as a spacer to set both rails 1/8" from the tailgate.
3. Clamp the rails. The T-slot rails use adjustable-back clamps built for the extra load: tuck each clamp's top jaw firmly into the top inside corner of the bed rail sheet metal, loosening the screws to reset the jaw if it does not seat, with both sets of teeth fully engaged. Fit the clamps between the adjustment screws front and back and tighten them with a 9/16" wrench while you push the rail down and tilt it up about two degrees, which Retrax says keeps water out best.
4. Square the rails. Measure across the rails on top of the front cover and again above each clamp; all three must match within 1/16". If they don't, remove the clamps, turn both white adjustment screws with the 6mm Allen wrench (one full turn moves the rail 1/16") and re-clamp. With the cover closed and latched, the weatherstrip should show equally on both sides; if one side shows less, move that rail forward toward the cab. Once the rails are square, loosen each clamp's jam nut, run the stand-off bolt in until its bumper firmly contacts the bed wall and re-tighten the jam nut; Retrax says not to over-torque the bolt.
5. Fit the drain tubes. Peel off all the protective film, push a drain tube into each side of the canister and turn it clockwise until it clicks twice. The tubes usually exit through a hole drilled in the factory bed plug, or another suitable hole, routed as directly as possible; if you drill a new hole, check for lines behind it first.
6. Check and re-check. Open and close the cover and the tailgate to make sure it rolls without rubbing or binding; on some trucks, raising or lowering the rear of the rails slightly improves the tailgate fit. Re-check that every clamp is tight now, after the first week of driving (a warranty condition) and now and then after that.