runs good at idle and atlow rpms,but rattles and backfires when its revved on 1997 Nissan Sentra

we changed the fuel pump and fuel filter,checked MAF operationa and it checked out ok.checked distributor and cap rotor and plug wireschecked fuel pressure w/ new pump (ok),checked TPS and MAP sensor, car looses power when it reaches 37 to 40 miles per hour acts as though it were starving for gas,what can it be? thhere are no codes stored in ecm.

Asked by for the 1997 Nissan Sentra
3 answers
possibly timing issue
Check for exhaust restriction. Possibly loose catalyst in converer.
could be fuel pressure to low or several other issues as stated.