Are you sure the gauge is reading right? Is it in the engine compartment? A lot of them get wonky when they get hot, especially the liquid filled ones.
Say, it was 7.5, made some passes, it got hot and gauge read 3.5 (but pressure was really still 7.5). Adjusted it upwards (actual pressure 10), hot gauge still reads 7.5.
Later, gauge cools down and reads actual pressure of 10 psi.
Just a theory. Have had/seen many problems with engine compartment fuel pressure gauges in the past. Would suck to replace something expensive and still be showing the same problems.