Check for vacuum at the vacuum modulator. check for vacuum leaks from the assist pump to the accessorys. does the a/c blow at the right vents. the assist pump is where the distributor would be in a gas engine (center rear)
Automobile(s): 1988 Allante' (sold), 1984 Eldorado, 84 Sedan DeVille
Re: 5.7 Liter Diesel trans problem
Could also be a stripped plastic governor gear. Or the weights on the governor stuck. Get a manual that shows how to access the governor. Its accessed from the trans case, located close to the tailshaft under a tin cover held in place with a snap ring.
What car is this? I don't believe it's any that you've listed. The first thing I'd check is the TV cable to make sure it's adjusted properly. It'll hang up on shifts like this is it's way out of whack.