Sluggish

1994 chevy s-10 pick up, 235,000 miles 4.3l

The symptom is as I drive the truck drives like it's starving for gas. It will hesitate while driving. The truck starts fine all the time. I did plugs and wires, I "cleaned"the cat converter. About 1 year ago I did a fuel pump for the 3rd time. The fuel filter has never been replaced. I did the fuel injection unit( I think it's the cpi unit) over 100,000 miles ago. There are NO codes. People have suggested o2 sensor or map sensor. Any ideas I want to keep the truck it's been great. It seemed to start on freeway driving at high speeds and I couldn't accelerate but it does it all the time now. Please help I need my truck back. :(