My 88 turbo2 used to run perfect sometimes,then other times it would lose power in high rpms and backfire.but when i push the pedal a little bit it will rev all the way up but be slow.now it went from doing it half the time.it does it all the time.i replaced the fuel filter,got the timing and coils checked.i have perfect grounds.i am thinking maybe the FPR? or the Fuel filter on the fuel pump? please help!