Clunk when let off gas @ 60-70 mph

[Tom P.]

Guys,
I'd appreciate your thoughts on this. Driving on the highway at 60-70 mph, I noticed a clunk-like sound when I suddenly let off the gas. It doesn't occur at 10, 20, 30, 40, 50 mph. Any thoughts why this is happening, or am I paranoid?
Thanks,
Tom

 

[Jon]

Could be any number of things from engine mounts to U-joints. Is it under the truck or engine compartment. Location is a big indicator. Never hurts to drop the drive shafts to check U-joint flexibility. How many miles on it?

 

[Tom P.]

There are about 145K on it. And it only seems to happen when I quickly pull off the gas when going 60+ mph. If it helps diagnose it, I also get an occasional clunk when I've come to a stop then let off the brake.

 

[LittleCaesar]

2wd or 4wd? If the latter, grease up your driveshaft using the zerk fittings and report back after some time on the road.

 

[Tom P.]

4wd... A year ago when I got it my mechanic friend greased it up. Not sure if he got everywhere. Anything else I should consider?
Thanks!
Tom