car hesitates/stutters upon acceleration...?

I have a 1990 GMC Suburban 5.7L. I just replaced the spark plugs, wires, dist cap, rotor, and fuel filter not even a year ago.

So if im sitting at a red light, press on the gas, the truck doesnt wanna accelerate like it should. Rpms slow down like its gonna stall, it starts accelerating real slow, then slowly comes back up to normal. It does this wether the engine is cold or reg operating temp. It only does this in first gear. And only does it on a loaded engine (wont hesitate when im parked and rev the engine, only if im sitting at a light or stop sign, then try to go).

As i said earlier i just replaced all plugs, wires, etc not too long ago. I checked for vacuum leaks when i got home today. Couldnt find any. Brand new Alternator, decent battery, coolant level is fine. It seems that the timing might be off a hair, but not much. I dont know what else to check! Any ideas???