Runs fine wide open, but not at steady speed

[mousetopher]

I am stumped. I have an 89 s10 blazer 2wd 4.3 automatic. While trying to maintain a steady speed it acts like its running out of gas. If you maintain steady pedal position, in about 3-5 seconds it'll come back, but start acting up again in a couple secs. If you punch it when it starts acting up, you almost immediately have full power. I have changed the plugs, wires, cap, rotor, the distributor (because i broke it), the fuel filter, the screen on the fuel pump (because I drained out some bad gas. It sat for almost a year). I have driven it about 300 miles so I dont think I can blame it on sitting. Any help would be appreciated.

[MT-2500]

Any codes or check engine lights?
Check fuel pressure.
Check the base timing by disconnecting the EST wire.
MT