UPDATE: Since my last post I checked all the grounds, fuses, and electrical connectors. I cleaned them all with electrical component spray, but they really weren't corroded. Then the mower wouldn't start. It tried but backfired louder than ever during several attempts. So then I went and spent $100 on the maintenance kit and replaced the plugs, (which were soaked and one actually fell apart,) replaced the air cleaner and prefilter, changed the oil, (yeah, I may have spaced out during the pandemic and didn't change it for a couple years,) installed new oil filter and new fuel filter. It started right up! Still, the temp gauge pegs on red after a minute of mowing, then quickly retreats when I shut mower off.
Still, I think it is actually overheating somewhat because the hood is hot and so is the engine compartment when I raise the hood. (More than normal for a sunless 70 degree day.) I haven't done the test with the radiator cap off to see if the coolant is moving, but I will tomorrow. Honestly, I have had this machine for 17 years and it's taken a lot of punishment so I am starting to feel the itch to get a newer machine. I also think the deck itself may be the issue. Can you lube inside that gear box? I couldn't find a way to do that, but I may have overlooked something.
I will report back again for those of you tuned in to my tale of woe. Thanks guys.