4T65E in 2006 Buick Lacrosse CX 3.8L, 2nd gear starts

[zzyzzx]

I believe we've FINALLY figured out the issue. Getting U1300 low voltage codes for some time

I'm adding your story to my long list of reasons to have a voltmeter in the car, even if it's only the type that plugs into an outlet that you use occasionally.