When the TCC started slipping it set a OBD-I code and turned on the CEL.

I was on a trip and I had the transmission rebuilt at an AAMCO on the East Coast of Florida.
The OD unit was not rebuilt then because AAMCO said they would have to wait on a part that had already delayed the trans 11 days.

Looking back I wish now I had the truck towed over to Fort Walton Beach Florida to Suncoast Performance.
The towing bill, the wait for the repair to complete, and the total cost would have been less, as AAMCO charged $3300 without touching the OD unit.
I had friends and a place to stay at Pensacola.

When the OD clutches started slipping, first only on uphill grades, it initially confused me,
because I would see rpms jump up suddenly in the Tach at the same time MPH on the Speedometer would stay nearly stable.
After awhile I experimented pressing the button on the dashboard that turns OD off and found that RPM and MPH now stayed normal.