I just bought this thing not too long ago and I have done a full tune up since then. (fuel filter, air filter, plugs, wires, cap, rotor) When I get on it hard, sometimes it will take off like normal. Other times, it will pull not quite as hard, then about 3700 rpm it takes off like it hit the power band and goes like normal. Other times, I can nail it, and it sounds like its flying, but I'm going no where. I think I may have it narrowed down to 2 things, fuel pump or something with the timing. Anybody ever had any similar problems like this? Any help would be great. I cant figure this damn thing out.

My '97 4dr 2wd blazer had this exact same engine set up, with the same mods and all, and I could slaughter my roommates '97 sonoma 2dr 2wd all over the place. Now this one can barely keep with him. I need to get this figured out.