'87 Ranger w/ 2.9, manual, and 4x4

So this truck has been a massive project in electrical gremlins.

Lost function of fuel pumps, turned out a ground became 12V somehow and a 12V became ground. Replaced wiring harness and it runs.

Was super cold-blooded and had a hesitation, so ended up replacing both fuel pumps (turned out to be the in-tank one causing the problem).

Now the truck starts and runs GREAT. Except when I give it a sudden power draw (such as when I initially turn on the fan or headlights or blinkers), there is a brief hesitation in the engine.

Things that have been done to this truck since I bought it:
Both fuel pumps replaced
Battery replaced
O2 sensor replaced
Belts replaced
Tune up (TFI module, plugs, wires, cap, rotor, and coil)
Water pump replaced
Wiring harness replaced
Computer replaced
TPS replaced (there wasn't one)
Battery ground cable replaced
Starter solenoid replaced
and I think that's it.


I'm wondering if the alternator is to blame (have to double check, but pretty certain it is internal voltage regulation), but I'm open to other possibilities if anyone has encountered the same problem before.

 

Fender mounter starter relay(solenoid) is the power distribution for the vehicle.
Follow Positive battery cable to this starter relay's large post, all the other wires on this post need to be clean and tight

Alternator is connected there as are all fuses in the vehicle.

Use a volt meter to test battery voltage with key off, AND with engine running
Key off should show 12.3 to 12.8 volts

Engine running should show 13.5 to 14.9 volts

While engine is idling turn on all lights, radio and heater fan to high
Voltage should not drop below 13.5 volts
If it does then either one of the three fields in the alternator is bad or the internal voltage regulator is bad