4 Wheel Drive/SUVs: transmission

Question
I have a 1991 GMC 1500 jasper rebuilt the trans 2 years ago i got off the interstate it ran fine noe it will not change to high gear at 40 mph it kicks into neutral fluid looks and smells good

Answer
John,

Before I did anything to the transmission, I would contact Jasper.  There may be a warranty, or they can tell you what the typical problems are with this transmission.
It sounds like a faulty shift solenoid.
Depending on how many miles you have put on the vehicle, in this amount of time is not a lot for the transmission, unless there is a faulty part.

Carl