Hi, im having a problem with my car. 1st and 2nd gear seem fine, but when it comes on boost in 3rd and 4th it seems to be holding back or cutting the boost.

Its a 90 mfi s2 engine, stage 2 turbo, cone filter, -31 actuator, stainless exhaust. The ecu is standard but the boost gauge seems to show that it goes to 11psi and then drops to 10psi, i thought that this might be the problem that the ecu or amal valve is cutting the boost back to a 'safe' 10psi ?

It has NGK (i forget the number) plugs in. when i first got it running i took the car out, didnt notice any problem with the boost but didnt drive it hard. ive since taken them out, regapped them to 0.8mm. (i think they were gapped at 1mm) is it possible its blowing the spark out ?

Or any other suggestions. Cheers.