Fuel starvation issue? Please help.

[natedogg]

I recently bought this 84 GMC cheap because it didn't run, needed a transmission and had been sitting awhile. Swapped in a used trans, new plugs, wires, rotor and cap. Fixed a few other things and started driving. Seem to run and drive great and then this problem showed up and has me stumped. Once the truck warms up and after a short drive it won't accelerate fast. It will speed up, but slowly. I put on a new fuel pump, fuel filter, carb base gasket and a different quadrajet that I had and didn't solve the problem. Also, I made sure the heat riser was fully open at full operating temp. Keep in mind that this truck is mostly original with a 305 and the ESC distributor still in place. However, all of the smog parts and converter are long gone. Any suggestions? Thanks for any and all help.