That is part of the food chain for the POS positive battery issue.
It's in #1 Son's place, but here is a short repeat.
There is a lead washer in-between the two positive lugs on the battery side post.
It is a one time use item and if not replaced, it will no longer be 'thick' enough to maintain holding
pressure.
That then becomes intermittent to create wacky behavior of all electrical. Even ruin the alternator by load dumping it.
The 'greater than 50 miles' kinda sorta fits. After a while it works loose again, and again, and again
Just one possibility. Could also be a bad gauge like you initially thought.
Thought they would have fixed the bare metal issue with the ABS sensor. It rusts and looses
electrical contact with the ground via the mounting surface.
There were TSBs on that on the old GMT400's and yours is newer.
Another possibility is that your sensor and gear (tone ring) are loaded up with metal filings.
Picture of my Ex's sedan when her ABS was acting up (light came on occasionally) and after dusting
this stuff off, it worked just fine
Close-up
