1998 Mustang GT hesitation in 2nd-3rd gears between 1.5 and 2.5K RPM

My car hesitates under steady throttle in 2nd and 3rd gears between 1.5K - 2.5 K RPM after AC compressor replacement.

One week afte I replaced and recharged my AC comprssor my car would start hesitatting under steady load. THe night it all began my battery would suddendly die. After jumpstarting it the hesitation started and my AC clutch would engage more often than usual.

Things I've already did:

Air Intake:

Replaced the air filter

Replaced the MAF sensor

Did a smoke test for possible vacuums leaks. None found

Cleaned the throttle body plates.

Replaced the Idle Air Control Valve

Ignition:

Replaced all spark plugs. Used Motorcraft Platinum gapped at 0.054

Replaced the wires. Used dialectic grease.

Replaced stock coil packs with new Motorcraft ones.

Fuel delivery system: 

Replaced the fuel pump

Replaced the fuel filter

Replaced the fuel pressure regulator. Still has 0 PSI with key on, engine off, 29 PSI at idle and vacuum line connected to the pressure regulator. 40 PSI when the vacuum line is disconnected. Clearly, I have low fuel pressure but I don't know what else could be the culprit in the fuel system given the already replaced parts. Relays and fuses? Voltage going tot he pump?

Thought about replacing the injectors but I don't think that would help. Leaking or clogged injectors would cause a more or less constant misfire. I might be wrong.

Sensors:

Replaced both upstream O2 sensors because I had codes for them. (had a lean fuel condiiton on bank 2 and rich condition on bank 1 at the same time. Codes gone after I replaced both O2 sensors.

Replaced the throttle positioning sensor.

Replaced the temperature sensor for the engine.

The misfire started one week after I replaced the AC compressor. Now I am thinking that it might be the crankshaft positioning sensor since it is located next to the AC compressor. I might have damaged it slightly or something.    I have no codes whatsoever. It idles well. Runs good in 1st, 4th and 5th gears. 
Comments (3)
No. 1-3
Chiper
Chiper

Thank you for your advice. How do I exactly pressure test the fuel pump? Increase the engine load to a certain RPM and see if it holds the PSI?

Chiper
Chiper

Thank you for your advice. How do I exactly pressure test the fuel pump? Increase the engine load to a certain RPM and see if it holds the PSI?

ScottyKilmer
ScottyKilmer

Editor

pressure test the fuel pump first to see iff it's weak. If not, have the fuel injectors cleaned and pray that fixes it https://www.youtube.com/watch?v=bKGI9N_yWd0