Clank noise when put into reverse or when releasing throtel at high rpms in any gear

If the clank ends with a creak, that's likely a U-joint, otherwise the sidegear to spider gear clearance in the 7.25 is probably excessive. If you stop now and tighten it up you may get a few more years out of her. But if you've been peg-legging it, she's probably done, cuz the next thing to go is the crosspin to case cradles. When they get "wallered" out, it's pretty much over.