Clunk when shifting from park to drive — 2012 Chevrolet Silverado

This is very common on GM trucks and usually NOT the transmission itself. The clunk is typically from drivetrain lash — the slack between components getting taken up all at once. **Check in order:** 1. **U-joints** — get under the truck and try to twist each U-joint on the driveshaft by hand. Any play = worn U-joint ($15 each, easy to replace). This is the #1 cause of the P-to-D clunk on Silverados. 2. **Transmission mount** — a worn mount allows the trans to shift position when loading/unloading. Visual check — look for cracked/sagging rubber. 3. **Transfer case (if 4WD)** — the transfer case chain stretches over time, creating slack. 4. **Differential backlash** — ring and pinion wear increases the gap between gear teeth. The telltale for U-joints: if you also feel a clunk when you tip into/out of the gas pedal at low speed, it's almost certainly U-joints. That load/unload cycle takes up the play each time. Parts stores will check U-joints for free if you're not comfortable getting under the truck.

My '13 Sierra did the same thing. Replaced both rear U-joints ($30 total, 2 hours with basic tools) and the clunk was completely gone. Those U-joints had zero grease fittings from the factory — they're sealed and once they start going, they go fast. When you replace them, spend the extra $5 each for the Spicer greaseable U-joints. Then hit them with the grease gun every oil change and they'll last forever.