Chrysler Repair: Electronic Transmission doesnt shift out of gear:, chrysler new yorker, output shaft

Question
I have a 1990 Chrysler New Yorker Fifth Ave front wheel drive
I changed the trasmission fluid relaced with atf 3 and changed the filter. The problem is the transmission does'nt want to go in overdrive and if i jack the passenger side front wheel off the ground in the garage and put the car in overdrive  and run the speedometer to 40 miles an hour and press cruise control the speed will race from 40 to 80 miles per hour then back to 30 per hour. could this be s speed sencor ? Thanks Ken

Answer
Hi Ken
I suspect that the run-up in speed and then backing off is simply because you have the wheel off the ground and so there is an over-response and then backing off by the cruise control. Besides, the distance sensor is being driven by the right output shaft and so the differential is being put to an extreme test, and almost anything can happen under those dynamics.
When you say it "doesn't want to go in overdrive" I suspect that what is happening is the engine controller has detected a fault of some sort in the trans operation and has put it into limp-in mode. That means the trans only operates in 2nd gear, and won't shift to 3rd or overdrive, but even if it does get third but not overdrive there is a fault of some sort that is aborting the shift. I would take the car to a Chrysler dealer or trans shop that has a diagnostic readout box(DRB II) and the data link plug (6 pins, three on a side, rectangular) to mate with the socket that is under the dash on the left side and blue in color. Ask if they have this DRB and plug and if so ask them to readout the transmission controller for fault codes. I have the shop manual for the electronic transaxle to compare against. Ask for the code number (two digits), the name of the code, what it means is defective, what is the nature of the repair and how much might it cost. Then write me back and we'll see if it rings true. They might even credit the cost of the readout against the repair, you might inquire, if you authorized the repair. But take your time to get the best diagnosis and quality of repair on this transmission because it will likely be expensive to the point of raising the question of whether it is worth doing. So if you put that kind of money into it you would like the job to be done correctly. A dealer or independent (non-franchise) shop with a good recommendation is needed.
Let me know what you learn.
Roland