2002 x type 3.0 with 119K miles. 19K on new transmission (by previous owner). Recently fixed vacuum leaks and is running good except the Gearbox fault light is still coming on. In cold (15 degree F) mornings starts and runs fine and I get to work with no light. Coming home, transmission starts shifting between D and 4 (you can watch shift indicator light go back and forth). When I get home and stop, I get the gearbox fault and the shift indicator light goes off. Sometimes it clears and I can go 10 miles without a light and when I stop it comes back. The next time it comes on at start and stays on. Had codes read and only have a p0420 even with gearbox fault light on. If I drive in 4, it seems to run fine. It shifts up when I start from a stop but will not downshift. Seems similar to other threads but the no codes has me stumped. Have done a visual on TCM and I cannot see any water signs and throttle body seems very clean. Original owner had the vehicle serviced frequently. Checked all grounds and cleaned them. Any ideas for a new member would be appreciated.