k2500 "clunk" at stop

[chevy23]

I have a 00 k2500 crew cab has 178k on it and truck runs nice and tranny seems to be healthy to me. When I come to a stop every once and a while their will be a loud clunk or thud that come from the rear. It will do it with the truck in park and turned off also if I walk a few steps away or put my debit card in the pump. I was doing some research and some said could be U joints but I figured I'd join a forum since I'm new to trucks. any ideas or help would be greatly appreciated.

[dodge123]

could be the slip yoke needs to be greased and is binding up. Do you also notice a slight jolt when accelerating?

[chevy23]

Not very noticeably. But a few other little things i notice is that when cruising 55-60 it is nice and smooth. But lets say I catch someone doing 45-50 it seems like it wants to down shift right away and starts to vibrate nothing drastic but a slight vibration then it will shift back into the high gear once I get above 50 or so. sometimes when cruising at 55 60 and you let off it decrease speed drastically it seems.