Diagnose My Miss / Hesitation

[North Coast Cab]

3.0 single plug w/46 PMO's. 10:1 50/50 race fuel
The first 5-6 laps the car runs strong with typical power coming on around 4,000RPM. As the lap count goes up the power band does as well. By the end of a 30 minute race my power band doesn't start until 5,500RPM's.

I have received some professional input from PMO and Clewett, but curious if anyone else has experienced this.

TIA, John