Ok ive been around lt1's a while and built several 10 second cam only cars so im no newbie, but im having some issues with one i just bought that I cant figure out.

The car is a 1996 Impala ss, completely stock with a asp piggyback pulley and madz28 tune.
I got the car with this problem.
The Car pulls fine until 4500, then falls on its face like a rev limiter, then will pull to 5000 or so, do it again, then pull again and repeat until the 6000 shift point. It does this every gear, but not till 4500.
It also does it in neutral with no load!

I got the car with new plugs, wires, cap/rotor, coil/icm, map fuel pump, fuel filter, and crank sensor. When i got it i replaced the opti itself, and the problem is still there. I also unplugged the maf and no change. No codes or history of codes either. No misfires counted.

Ive check fuel pressure while driving and wot and its steady at 45psi, did a volume test at idle and it is ok.
Im lost as to whats causing this, anyone got any ideas?

 

After reading your post the first thing that came to mind was the opti & fuel pump because that describes the exact same thing that happened with me with surging rpms. From their I would check the injectors for adequate voltage then compare the timing chain or hub mark to TDC on the #1 piston, if that helps.

 

It has a new opti and new fuel pump...neither affected the problem

 

Even though the coil and icm are new have you checked them? Have the icm tested and also check the coil since they can fail or give weak signals under load or when temps get up. Could also do a compression test on the cylinders.