I just had to pull my car off of the dyno 2 straight days...Fuel pressure was dropping and after the first day put in a new pump and went back, but was still getting fuel pressure drop...Turned out my voltage was dropping down into the 12's under heavy throttle...I assume the alternator is no longer keeping up....Nick have you ever seen it a wiring issue when voltage was dropping??I have had issues with after market alts at 6-7000 RPM as the output drops to 12.0 or so.
After replacing the pulley with a stock one which gave better output, but still output drops over 6000 RPM.
After discussing this with an alt repair shop, I was informed these alts has a built-in limiter which drops off voltage at high RPM.
I use a volt booster which gives 14 volts at RPM, but I now use an aftermarket alt with a stock pulley and a life time warranty, as the alt last will only last a year or 2!