Car seems to run strong in the low and mid range RPM, but breaks up bad at around 5000 RPM. I have ODB1 and TTS Datamaster, as well as a file if anyone is interested, but no codes were thrown. I thought it was the coil and just replaced it with a Crane Unit, problem wen't away but came back only worse.

Other symptoms include:

1. Difficult to idle until it has warmed up, this was never a problem before.
2. Increased backfiring, especially if I let off of the accelerator. I've always had a bit of a "gurgle" in this situation, but it has definitely increased.
3. Severe "breaking up" starting at 5000 or so RPM, car pulls strong until then, but almost hits a wall and begins to sputter severely and sometimes backfiring. Major loss of power.

Opti is low mileage, <10000, AC Delco Plat plugs < 10000, Taylor wires, Brand New Crane coil.

Car has modified heads, CC305 cam 1.6RR, Hooker LTs w Heated O2 mod, K&N Fresh Air and a BBK 58mm TB

Just want to know where I begin... Any suggestions greatly appreciated.

 

Why don't you replace the fuel filter and monitor the fuel pressure with a gage taped to the windshield. Also while your hooking up the gage, pull the vac line off the FPR and see if it's wet.

If it turns out the fuel pressure is low and you have been running lean, the next thing you want to do is a leak down test.

And oh BTW the 58mm throttle body isn't doing you any good. Have you had your PCM reprogrammed for better fuel delivery?