the voltage gauge did not drop any voltage period. just saying

depending on engine serial depends on what 50 amp breaker is used and he reports they have been changed ? Yes the yellow flag breakers are problem childs. That is correct you can by pass that for testing - but I doubt you even have or had the yellow flag breaker most likely the 50 amp red push in breaker -- is that correct ?

TPS and IAC has nothing to do with this problem period. zero

5 Volt circuit I can agree upon as the crankshaft position integrated with splice 101. (5 v transducer power for sensors) also tach lead 114 wire splice. Hopefully you have the manual PCM 555 manual and wiring diagrams for your app. I would not rule that out as you can watch that with the scan while running or record it. Most will read 4.99 v keep an eye on that when running to see if it stays steady or drops . Also the ignition circuit can be check = crankshaft pos. sensor tan -- black/brown -- grey leads

I would check easy stuff first that was mentioned - I am saying again to really check out the spark plug wire(s) can cause this or even at the coil tower - been there just to bring up again. No codes never shown up and I would not count on any with this form of running problem.