88 IROC Z-28 305 TPI 5 speed. The car free revs fine most of the time but some times i get to about 5000rpm and drops to around 3800rpm and sits there bouncing back and forth between 3800-4400rpm with the pedal to the floor acting like it has a rev limiter which it does not have. The other problem is under a load no matter what gear after 1/2-3/4 throttle it just falls on its face but hold the pedal to the floor and it does the same thing as when not under a load. I installed a fuel pressure gauge and it reads 47psi not running, 40-42 running, I tried to get the motor to fall on its face free reving with the gauge installed to see what the fuel pressure did but of course the car wouldnt do it. but when i do rev to around 5000rpm the fuel pressure drops to below 20psi.
Keep in mind that i have cleared a couple trouble codes 22 (TPS voltage low) 36 (MAF burn off relay) then 2 days later code 21 (TPS voltage high.) I think the TPS voltage was jumping around because of the hypertech PROM chip that i installed, but the engine performance has never changed it just wants to fall on its face. If it keeps this up I might be tempted to put the 510ci big block i am building for my 96 dually pickup in this car that just might teach it a lesson.

 

"but when i do rev to around 5000rpm the fuel pressure drops to below 20psi"

sounds to me like you answered your own question

but as rob said....check your coil, and while you're at it, the coil wire and plug wires.