I barely purchased a 96 Z28/M6 today and it has a few Mods
SLP headers
Flowmaster exhaust
Trick flow air intake elbow
that I can tell for sure it also "supposedly" has a CC306 cam tuned and installed by TSP(texas speed & performance)
is there a way to check if this is true without disassembly?

Problem is the car is idling at around 1900-2000rpm, it is VERY strong down low, but when you start to rev higher than 4000rpm it starts to sputter and lose power.Also I don't know if it is related but the speedo seems to be off as well.
Could this be a faulty opti?
faulty tps or speed sensor causing this?
And I can not find any vacuum leaks.
And also I have a second LT1 engine, harness and ECU w/4l60e out of a 94 that I was going to install into my 88 IROC, but I decided to keep out to build for my 96, could I try the opti and/or ECU off of it?
thanks in advance for any help you can lend
-Daniel