Extang Trifecta Signature 2.0 Soft Folding Tonneau Cover for 2014-2019 Chevrolet Silverado 1500/2500/3500 / GMC Sierra 1500/2500/3500 (6'6" Bed)

Here's the short version. Follow Extang's install sheet (below) for your truck's exact clamp positions and hardware.

1. Check the bed caps. If a plastic bed-rail cap hangs below the sheet-metal flange, trim away enough of it with a utility knife that each clamp bites on bare metal. Extang names 2004-2014 and 2021 F-150s and 2009-2019 Rams as the usual cases. Don't cut or scrape the bed itself.
2. Set the cover in place. Lay the folded cover over the cab end of the bed, unfold it and shift it until it lines up at the cab and the tailgate, then fold it back up without moving it. Note where the front clamps sit.
3. Tighten the front clamps. Seat each Jaw-Grip cab clamp under the metal bed flange (not the bedliner lip or a plastic cap) and turn it by hand until it touches, then two more turns. No wrench, and don't overtighten.
4. Close it and latch the rear clamps. With the tailgate down and the front clamps tight, unfold the cover fully. Swing each rear clamp down out of the cover rail, slide it at a slight angle as far out toward the bed rail as it goes, then pull it straight down and let go so it hooks under the metal flange. Latch both sides.
5. Attach the tethers. Open the cover. On a bed with plain metal flanges, clamp each tether (it hangs from the cover bow) to the flange and tighten the knob. On a bed with factory cargo rails, slide the supplied block into each rail, pass the tether knob through its lock washer and bracket into the block, move it up to the front bow and tighten. Do both sides.
6. Recheck after a week. Re-tighten the front clamps and tethers after your first week of driving, and check them now and then. To drive folded, stow the rear clamps in the rail before you fold the second section, fold it to the cab and buckle both straps.