I had mine checked over after a rebuild last year and found that it was leaning off at about 5500rpm.
a quick check of the fuel pressure found that it was never reaching what it should (only running 16psi on standard yellow injectors and stage 1 chip) and couldn't hold the pressure it was achieving either.
fitted a new fuel pump loom and a Bosch 044 (more overkill) and it now runs a treat.
the guy doing the diagnostics said it was more than likely to be the loom that needed replacing as it couldn't deliver the full 12v to the pump rather than the pump itself but did both while I was at it