Only other thing I can say is check everything. Where did you say you think it's coming from again?

 

A lot of times it sounds like its coming from the rear but sometimes it sounds like the front. Its extremely hard to pinpoint. But i really think its from the rear. The only thing that looks sketchy is a bushing for the passenger leaf spring but im not sure how that would do it and why i cant replicate it from jumping on the truck vigorously if it was the leaf spring

 

What I would do then is Jack up that side and then drop it quickly to see if the sound shows itself. Maybe the whole has to articulate to.

 

I think I found the problem. My rear fuel tank strap with rotted out and barely holding the tank. I can push it up and down. Maybe the sloshing of the fluid is making it bouce against the truck?

It just doesnt quite make sense because the sound seems like its coming from the passenger side and if it was the gas in the tank sloshing around, how come it only happens again after I come to dead stop and take off and not when I accelerate real hard..

 

Momentum. Not enough power to get a hard acceleration when moving.