K10 thumping feel

[82chevy350]

So on my k10 i recently installed
4 inch lift springs front
3 inch lift blocks in the rear
New trans mounts
Rebuilt driveshaft with extra 2 inches of slide room 1 inch in and 1 inch out along with stock movement
Transmission and transfer case
Rebuilt torque convertor



My problem Is when i accelerate going up a hill or almost flat surface i got a little vibration along with thumping feel right under my seat as i hit a small bump like somethings loose... The vibration isnt that bad but i figured it would be gone since i put new trans mount on.. But when i left off the gas it rides as smooth as can be with no vibration or thumping feel when going over bumps... Any ideas? This happened before i put another trans and transfer in it btw

 

[crazy4offroad]

unds like double cardan joint in the front driveshaft binding, does the truck have an NP203 t-case? Chock the rear tires and jack the front of the truck just high enough off the ground by the bumper so the front axle droops, leave the tires on for safety. Put the truck in neutral and try to spin the front driveshaft, see if the double cardan joint is binding.

 

[82chevy350]

Front driveshaft is out my 203 has part time kit i found the left rear body bushing has a gap could that be it?

 

[JimboFen]

What was the issue? I'm getting the same feeling in my 75. Clunking over small bumps that I can feel in my seat. Stock height.