Chrysler Repair: Le baron transmission, coolant temp, engine coolant

Question
I have a 1990 Chrysler Le baron Dr with 3L V6. I purchased the car last week and the transmission was in limp mode and had a bad speed sensor. I replaced the speed sensor and fluid (with correct mopar atf 3), There is no fault codes being displayed. The transmission wont shift into fourth gear, when i hit 73+ the car shutters and feels like its trying to shift but cant. The car runs very smooth up until that speed. I don't know what else to check. Thank you for the help.

Answer
Hi William,
If by no fault codes you are referring to the ignition key/check engine light approach then that result is not surprising. There are a separate set of diagnostics and two-digit fault codes for the transmission which are only obtained by a readout with a Chrysler DRB II or equivalent reader. I am not sure if in the '90 there is a separate diagnostic connector for that car (there is if have the 4dr car). If there is a separate connector it would be blue in color and located in the cabin, under the dash by the fuse box or perhaps behind a small door at the lower left end of the dash. It has 6 pins, arranged 3 on a side in a rectangular array. If you can get that separate readout, find out the fault code numbers, what they mean, what they recommend, and how much? Then write back and we can compare what you were told with the manual.
The only simple reason for non-shifting into overdrive is if the engine coolant temp sensor is reporting a too low temperature of the coolant (or it is truly too cold).
Roland