Dodge turbo diesel
New trans but old did the same. Won't always shift from 3rd to 4th. Diagnostics says trans temp is -90 degrees. Changed the ECM worked fine for about 2 miles then back to same problem. Previous trans had two new sensor strings installed in it before changing to a performance trans. Problem persists. Has new Throttle position sensor. When I let off the gas (diesel) completely and wait it will shift into 4 and lock up. Otherwise won't do it. Two trans shops and a bunch of money have failed to solve the problem.