It runs fine at 8psi all the way to 8000rpm. But under load it misses. Is it missing above 8psi under 8000rpm?
The only difference is boost pressure reference to the ecu and msd dis4 (does it use a pressure reference?)
I would be thinking some limiter is being activated or wrong tuning setting. Both of which I am sure the guys at unigroup would have picked up on.

Fuel pressure is good and A/F ratio is good too. What is happening with the A/F ratio when its misfiring?
Silly question but where is the fuel pressure reading coming from? The fuel rail? or fuel line? Is the problem not something silly like a mix up with the fuel supply line and the fuel return, being mixed up between the regulator and the fuel rail?