Nissan Repair: Stumble Problems, mass air flow sensor, mass air flow

Question
Need Help any ideas welcome and Thanks ahead of time! Ok I have a 1987 300 zx non turbo, v-6, 5 speed. New oil pump, timing belt, plugs and wires cap button, new head gaskets worked heads intake upper and lower etc. Ok here is the problem it stumbles between 1400 and 2500 near to the point of shutting off. Acts like (A) lack of fuel or and (B) lack of air. Cleaned mass air flow sensor, Checked Belt timing, Checked distributor timing, set at 20 before top dead center, Checked idle set at 700 rpm, Replaced all Vacuum lines, Checked to make sure no vacuum leaks, has 35-45 p.s.i. parked fuel pressure. Has good exhaust pressure, will idle and rev without stumble but under load as driving stumbles.

Answer
Hi Paul -

This sure sounds like the fuel pump. I know you checked the pressure, but I would like you to check the volume.

Disconnect the fuel line at the engine where you can place a jar or container under it. Turn the ignition on for 3 seconds. There should be at least a cup of fuel in the container. If not, then the fuel pump/and or filter needs replacing.

Hope this helps -
aloha
Calvin