Clark

Hey all, I'm new to the Nissan world but i am diggin your site. So heres the story maybe someone can help. I swapped a good running v6 3.0 from one shitty lookin 87 p-up to another much less shitty 87 p-up. Only a 4cyl came out of the less shitty p-up. The first truck (V6) ran great when I brought it home, I swapped them and things got wierd, when you start the truck it runs and drives great for a while, until you get off the gas and try to accelerate again, then it bucks and cuts out real bad, like whiplash bad at about half throttle. But when you pull over shut it off, It fires right back up and is fine,takes off great, until you get off the throttle again then same thing. I have read about the EGR alot on this sight, but i guess what stumps me is that the motor ran great 2 days ago in the truck!! Could this still be my prob?
This truck has no smog equipment on it anymore, is that a factor? Here is my have done list but to no avail.

ecu diag Shows fine
fuel pressure test, 34-35
plugs,wires,cap,rotor
swapped the computers
swapped all the fuses on the fenderwell
checked vacumes
swapped tbi's

guys I am lost here, I wonder if there is some sort of fuel relay in the mix somewhere? If so where? any help you can give me would be great!!!!