I had the trans in my 95 b2500 van rebuilt last year, I have only been driving locally. Today I got on the highway and I have no overdrive. The button on the dash makes no difference. What all could cause this? The trans works great other than that.

 

If the transmission is a 46RE I would recommend checking the wiring to the transmission for damage.

There is an overdrive solenoid located just inside the pan and it may have failed. It is relatively easy to replace this but I'd check the wiring before diving in and pulling things apart.. Search on youtube as there are several good videos that detail the overdrive solenoid, governor solenoid and governor sensor replacement.

If you don't have a 46RE electronic transmission but you do have overdrive, you might have a 46RH or A518 which is a completely different animal with which I am not familiar. It might be a simple cable issue. Perhaps someone else here who has delt with that trans before may be able to assist you better.

 

Most likely the rebuilder reused the OD drum and it has now cracked.

 

Could be the powertrain control module, valve body or the piston like Alloro had said. But I would hook up a 300 psi gauge in the overdrive port and see what your line pressure is and go from there.

 

Trans is repaired. Had a sticky valve, works great now.