Transmission in 91 DeVille just would not shift automatic trans
Did you check fluid level, check it when the car is running and hot. If that's is OK then it could the shift solenoids then it would need to go to a good tranny shop.
There is a big fuse in that panel under the dash, along the back of the floorboard that can cause a similar problem, Seems it will blow when the air compressor goes out for some reason. I had to have a transmission mechanic tell me about it , I had no idea there were fuses in that location, I thought I had serious transmission problems..
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