My 91 Dodge Diesel 2500 2 wheel drive automatic with overdrive floats between overdrive and 3rd gear between the speeds of 67-72. The truck has 175,000 miles on it and is in very good shape. It does not do it all of the time but seems to be more prevalent early in the morning after the truck has been parked overnight. A mechanic has told me it might be the speed sensors which are located on the outside of the transmission. Please advise.

 

If the speedo is steady while this is happening, the speed sensor is OK. I'd lean more towards a TPS problem. Take a look at the sticky thread at the top of the 1st gen forum, there's info on TPS adjustment, cleaning, and low-buck replacement.

 

check your tps (throttle position sensor) see if its in spects. or has a bad spot. i also seen temp sensors cause this. overdrive on this unit is controlled by the computer sending a ground. check speed sensor and tps. if all els fails check signnel to sensor from computer ans see if the computer is turning off od.