Jeff, thanks for the video - it now explains it all.
That is indeed excessive "hunting" or surging. I suspect that the controller is seeing the 100-200 rpm surges that it knows it has not initiated itself and is eventually tossing the 25 code.
At this point, if I had the unit here with me, I would open the cover back up to perform one more test on the governor before looking at the fuel injection pump itself.
1) While it's surging, watch the governor arm and injection pump control lever very closely - it's important to know if the fuel rack OR governor is actually moving causing the surge OR if the fuel rack/governor is absolutely stationary while it's surging. It is possible the actuator arm has slackened and has a lot of "play" between it and the injection pump.
If the actuator arm going from the governor to the fuel injection pump is absolutely stationary while it's surging then your problem lies within the injection pump itself.
94-Newmar Kountry Star 40-KSDP
Spartan/Cummins 8.3C-300HP/Allison 3060 WTEC-II/25yr RV Tech RVIA Certified/Onan-Cummins Certified