Sep / 17

1992 isuzu npr diesel transmission not shifting?

                        It has the 4bd2 engine and the jatco jr403e automatic transmission. Truck ran fine on friday got in it monday morning and it will not shift past second gear. Reverse is fine but you have to hold it to the floor and back off a little to get it to change from 1st to 2nd gear. It pulls fine with no slipping in first and second. Transmission fluid if full and clean. This transmission has less than 8000 miles on it. I hope this is a sensor or electrical problem. All wiring and connectors look fine. TCM shows no codes just a steady  continuous flash when the test connector is jumped with a wire. Any help would be great.
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