I have a 2003 F350 diesel, 4WD, Auto. Not a lick of problems until this morning. As I came to a stop I heard a "clunk". Then the OD light started blinking, the Check Gauge light came on the Transmission Temp Gauge pegged at "HOT" and the transmission started to shift harsh and fast. "Fast", as in, through the gears very quickly. I stopped and checked the fluid. Not overheated nor burnt. I drove for a few miles stopping occasionally to check the trans fluid and it never overheated. After a few stops it started to shift normally although the other symptoms remained. I parked it and let it sit for several hours. Went back out and it drove fine (no lights, etc.) for approximately 10 miles and then it all started again......... Everytime I let it sit for awhile I can drive it with no symptoms, however, they do ultimately return. I talked to a friend who suggested that the rear diff speed sensor may have gone bad, but my speedo still works so I doubt if that is it.
Any comments/suggestions will be greatly appreciated.

 

If the OD light is flashing, then there is a code stored in memory that needs to be scanned and diagnosed.

 

Thanks Mulletman.... It turned out to be the Transmission Temperature Temperature Sensor. It had a short and would intermittently peg (high) the temp gauge which in resulted in the transmission controller going into to fail-safe. Nothing that $261 couldn't repair!