I have a 1996 Trans am and just recently it started sputtering badly under acceleration, mostley if @ 1500 rpms. After 2,000 it begins to gain power quickly though. I recently changed the spark plugs and wires and had to remove and reattach a header to do so. Also its been pretty warm here in L.A (around 90) just in case this might attribute to the problem. I already added a fuel injector cleaner to the gas tank but it doesn't seem to be helping and I'm going to clean the throttle body, any other ideas?

 

Does it "sputter" when cold as well? or just after it has reached operating temperature?

There's no harm in double-checking all the plugs are in good and tight, as well as making sure the plug boots are seated properly(or if a wire had been burned). Cleaning the throttle body might help, but I have a feeling it won't for this situation.

 

Look at your coil and ICM. A lot of stuff can start to mess up when things get hot. Search for ICM Cooling Mod.