Clunk when putting in gear...

U-joints?

With your foot on the brake, put it from drive to reverse. If it clunks, like you described, your U joints are shot.

In order of easiest to hardest to repair (funny it also cheapest to most expensive) Worn u-joints, broken exhaust hanger, busted engine and/or tranny mount, pinion gear bearings worn, excessive ring gear to pinion gear clearance.

Whitelightning

Pull the drive shaft and lube the slip yoke with GOOD synthetic grease, While under there check all the U -Joints.