When I put my truck in gear it clunks HARD. I got under there and twisted the driveshaft it felt tight. I am however going to change the U-joints.
The the pinion seal is leaking on the rear axle, so could this be rearend issues?
If this is rearend issues a new pinion seal and making sure that the yolk is torqued properly fix it?

 

Sorry I forgot 88 4x4 short wheel base 8.8 c6

 

Kind of a tuff one to answer without more info. Like,,,,,does it clunk when the engine is cold and idling high? How many miles? Myself I would put the rear end up on jack stands and move things around to try to isolate where the clunk is coming from. If I had to guess I would say worn ring / pinion gear, excessive play will cause a clunk.

 

Yeah a clunk like that usually means bad u joints or too much free play in the gears.