5100 rpm and it quits

I recently purchased a 1993 cobra. I bought it from an individual that bought it as a roller (no engine or tranny).
The previous owner did not know much about the engine that he put into it. So in turn , I do not.
Here is what I do know.
Stock block.
Stock heads (not gt40) stock
Has aftermarket cam (unknown what) but I can tell it does have a cam.
Edelbrock performer intake
T-Rex external fuel pump
75 mm throttle body
24 lbs injectors , with calibrated mass air meter.
Mac Headers

The car rums very strong until the RPM’s hit 5100 and the engine gives up. It is not hitting a rev limiter, it just pops and sputters.

I have a two part question
1. What kind of heads should I buy
2. What could be causing the car to run out of steam at 5100 RPM

I have checked the timing and the vehicle does the same thing regardless of the timing.
I have adjusted the fuel pressure regulator from 40psi to 80psi with minimal difference , regardless of my adjustments at 5100 RPM its (game over)

Any suggestions?

Thanks for the input. I am going to get some AFR heads this weekend , should have them installed in a couple of weeks. I will let you know if that works.