2005 Chevrolet Silverado clunking

This sounds like a strong symptom of a bad engine mount or transmission mount. I would definitely start there to make sure the bushings aren't broken.

There's could be solenoids and such that control shift points that might cause a hard shift but anything else you would typically start hearing noises or the car will drive really bad.

A bad front or rear typically wouldn't cause a vibration depending how bad they are while driving. Front and rear mounts are usually roll stoppers which means they're main job is to hold everything in place from moving front or back. Putting a car into drive or reverse is a big load because you're engaging the transmission at that point and torques the engine which may be your cause of the clunk. Check your engine mounts and let me know what you find.

No problem.