Traction Active lighting up in 2002 Venture

Sorry for the multiple questions, but when it rains, it pours.

2002 Venture,3.4L, 105,000 miles. Traction Active light has been coming on whenever we drive the van in reverse down our driveway (short downhill) and any other similar downhill. No debris or leaves. Dry pavement does it. we get the familiar ABS feel through the pedal and a buzzing sound like the ABS has come on.

Recently took it to the shop and they checked the brakes. Rear brakes still have plenty of life left on pads and drums. Front brakes needed new pads and rotors. This fix didn’t make the problem go away. Shop said no codes were stored. They said they could check the ABS manually for aobut $150, but most likely test would be inconclusive as it could be either the ABS Sending Unit or one of four ABS brake sensors (my wife and I have a hunch it might be the rear, possibly driver’s side rear). Has anyone else had the “Traction Active” light come on when it really shouldn’t for extended period of time? Any suggestions on where to go w/this problem?