My 4.0 will flash the engine light under heavy load at high rpm, 5500rpm plus (P0300 code) It did this on rare occasions when it had just a Bama tune. I just put long tubes and a cai on its become a regular thing, I've set the code as low as 4500 rpm in higher gears after running it hard through 2nd and 3rd. Used my livewire to read frp, typically 45 on cruise, 60ish at idle. Normal acceleration 50-55. Hard acceleration 40ish and the light would flash. Changed fuel filter and some inj cleaner I'm seeing lower numbers. Idle is 50ish cruising it hovers over 40, hard throttle I've seen as low as 35. Off throttle high rpm and load I've spiked as high as 75. All this irregularity has me concerned. What's a safe frp? Suspecting my fuel pump.