...I just figured out yesterday what was wrong with my Magellan (I think)

Rust

The power connector to the side of it seemed to have some discoloration; I had examined it closer yesterday and started cleaning it with WD40. Seems that some surface rust was present.

Plugged it back in and it didn't misbehave at all for the entire day of riding. So I think that the unit was not getting a good supply of juice and that's why it was going bonkers.

What makes matters worse is that I ordered and received a replacement Garmin Drive 51 LM 5 GPS yesterday Now I gots two

https://www.bestbuy.com/site/garmin-...=ref:212,loc:2

I'm going to clean both of the male and female power connection areas with some electrical contact cleaner today, and then follow up with a nice glob of dielectric grease to protect it. Should have known to protect that connector from the elements; after all this GPS is not "weatherproof" as was aptly demonstrated to me.