I just bought the truck, 91 d250 auto, and I have surfed through here quite a bit. I did find that the VSS caused the no overdrive and speedometer problems for some guys. I changed that and well it didn't help. Now I will admit I didn't check the wiring very good from the sensor back to where ever it goes. So if I need to start there fine, if someone has an idea I would like to hear it. Oh yea the oil pressure guage donesn't work either. And the coolant never reached operating temp so I think that is out also. Otherwise man I love the truck and I will welcome myself aboard as finally owning a 1st gen and I appreciate the all mechanical make up. It is a far cry from my 03 but it is a work in progress. Thanks to all for any opinions or ideas. Aaron

 

Welcome to the family. Did you check the fuses? Also look at the big plug on the back of the instrument panel that feeds all of it, wiggle it around and make sure its pluged in good.

 

Also check the bulkhead connector where the wires go through the firewall, sounds like a loose connection.