I had my 727 rebuilt last year by a "professional" trans builder that specializes in mopar. That POS rebuild made it about 5 miles before it lost 1st gear and slipped through 2nd. Reverse was also gone.
He re-rebuilt it as a warranty. He blamed my new PTC converter, new pre bent cooler lines, or my new HD cooler as the issue. The 2nd build made it a few more miles (about 10) but it locked up on me at ~35 MPH on a backroad and actually locked the rear wheels up! I spun off into the grass and had to get towed home.
