My 2005 F-250 6.0 Diesel with automatic trans won't shift unless I let of the accelerator. The trans fluid is clean and smells fine, even before I had the filter and oil replaced. The trans pan showed normal wear in the bottom when removed as well as the filter looking good too. The truck has 189181 miles and the engine runs fine. When the pan was off I saw numerous electrical solenoids servos etc. in the valve body. Might something electrical be my problem. Help if you can!!

2WD or 4WD?

Check for codes and pending codes. It could be related to the Transmission Speed Sensor, particularly if it looks like a typical Ford Transmission Range Sensor (TRS). They are a high wear component. Other than that, I'd focus on the Transmission Input Speed Sensor and the Transmission Output Speed Sensor. Heat is the enemy of these Hall Effect sensors, which can cause, over time, cracks to develop in the sensor. This can affect the wave form generated by the sensor.