I am getting a strange clunk at about 5-10 mph when in drive. It feels like I am hitting a small speed bump. I have checked the u-joints and they all seem tight. If I creep up to speed going VERY slowly it doesn't seem to clunk. Its only when I takeoff at normal speeds. Otherwise, the truck drives very good with no vibrations or anything unusual. Does anyone know what this might be?

 

Engine/transmission supports? Maybe a bushing has finally worn through? You might also check front suspension components. The lift on the front end under torque can make the sway bar links clunk, track bar move etc.

 

Lil Dog.....Is it common for engine and transmission supports to wear out on our trucks?I never replaced mine but when I shutdown the motor sure gives the truck a good shake....

 

Common? Not sure.. but anything is possible. My old 89 tore the drivers engine mount in half on a startoff towing. Jerked the stick out of my hand!

 

Look at the front control arm bushing.