It's a 1991 na. The only modification is a header. My engine codes are for fuel pump relay and narrow range tps. But when I check with multimeter they are both in the correct range any advice.?
it only does it after warming up to operating temp and it loses power when you ease your way up to higher rpm.

 

Check the TPS resistance at the ECU connector that way you're taking into account the related wiring. Next check fuel pressure and the voltage at the fuel pump.