Guess I should have specified, but my truck is a 2WD with the 2 piece drive shaft. A slip joint is the joint between the 2 shafts and that is what I greased and what cured my clunk. I really know nothing about 4 WD setups.
I guess this could also cure a clunk if done at the yoke where the shaft connects to the transmission or transfer case if there is slop there? Not really sure about grease in the transmission or transfer case and whether it would harm anything but I kind of doubt it. Would think that as long as you don't go nuts with the grease, it would just stay on the splines.
2002 Chevy 2500HD Crew - Original owner - 410,000 miles so far. All stock with the exception of a lift pump.