power loss after prolonged boost

[Gixman05]

Hey everyone having issues with my 04 3.0d. under prolonged boost periods (22.3psi towing a car trailer or full throttle through 4 to 5 gears) the boost drops of slowly to 16 psi which feels like half power. When the issue starts the mass air flow value stays constant but the fuel rail pressure drops from 1380 ish down to approx. 700 bar. theres a lot of fault codes which keep appearing which i`ll list at the bottom. my injector value read are very similar across all cylinders (230ish) except for no4 it is (0) same with my selective mass adjustment all cylinders are similar except No2 is overcompensating a lot. Not at any time did the car go into limp mode or display a fault on the dash. except for the loss of power there are no other performance issues with the car.
AS far as I know the only deletes are the egr and the exhaust is straight through pipes from the turbo and not sure if it has been flashed or tuned.

fault code 4b90 injector rail monitoring seems to match when the issue arrises the rest seem to happen regardless.
4203-(0101) mass or volume air flow circuit range performance problem.

4ba0 (0113) intake air temperature circuit high input

4507 (0402) Exhaust gas recirculation flow excessive detected

4501 (0401) Exhaust gas recirculation flow insufficient detected

4B10 (1278) Accelerator pedal position sensor1 circuit high

4521 (1296) cooling system malfunction

Im not familiar with these cars at all and are hoping someone who is can unjumble this cluster fark of issues

Any help or direction welcome

Cheers Russ