39E is that the primary engine speed sensor or wire has a problem. The primary speed sensor is in the injection pump, Check the 6 pin connector to the injection pump, look at the wire ends to see if there ok on both sides, connector wires B and A. Check with a ohm meter between B and A for 600 to 1500 ohms to the pump.
Could look at the speed sensor on the engine, take the connector off and look at it, this would be a 44E code.
Don't understand why going down the road will do this.
Had a 8300 tractor that the primary sensor was bad and the code was always on, the sensor in the pump was bad and replaced the injection pump.
Everything seems to be tight where they both mount but are wearing on each. It wore the crank assembly on the top completely off ? I wouldn't think they should even touch each other? Did take belt off to see if the back would turn freely even with the top out but turned very hard by hand . DID...