slow acceleration

I have a '88 C-1500 with a 5.7 and 700r4 trans. The engine and trans got replaced a little over a year ago and has had no trouble since, but recently I have had hard times accelerating. The RPMS will only increase a little when I mash it. There are no trans problems but I think it is either the fuel system or lack of spark even though it runs fine at a constant speed.

check the catalytic converter, and muffler

Check your spark plugs....and then your cat-converter

I have the same problem in my 89 C1500. The main problem in mine is that the distributer cap and rotor are more corroded than my dogs butt. Check your plugs and see if they are chalky white, then i would check your cam and your timing, only after you check the Cat and your exhaust though. Good luck.