Chrysler Repair: 1993 New Yorker trans problem: harsh downshift, transmission control module, shaft support

Question
Hi..I have a 1993 New Yorker 3.3 with the 4-speed auto trans. It has onlt 47,000 miles. The trans delays and downshifts hard from 2nd to 1rst most of the time. Had the solenoid replace, no fix. I think it is the transmission control module. Can get one for about $130. Can I install this, and is it located on the tranny? Do you agree this could well be the problem? Thank you for being here...

Answer
Hi Wes,
The causes of harsh downshifts are numerous: engine idle speed too low, aerated fluid, low fluid level, filter cloggged, faulty pump, hyraulic pressures too low, valve body leakage/malfunction, input shaft seal rings worn/faulty, worn reaction shaft support seal rings, incorrect gear shift control linkage adjustement, worn accumulator seal rings, damaged clutch seals, worn clutches including the underdrive clutch. These are from the '92 trans manual which no doubt applies to your '93.
In light of all those possibilities I would not invest in the module yet. It is located on the right side inner fender shield near the front of the engine compartment (rectangular box with 60-way connector plug).
I would consider two things first:
get a readout of the transmission control module memory for the presence of any fault codes. This is done via a plug under the dash that has 6 pins called the data bus plug/bus diagnostic connector. It is NOT the plug under the hood for the engine controller. You may have to hunt a bit for a shop with the plug and reader, or go to a Chrysler dealer. If you get any code numbers ask for them, what they mean, what they would repair and how much. Then write back and we can compare notes with the manual I have. See if they will credit the readout against the repair cost if you decide to go with their proposal.
Second, I have heard anecdotally that changing out the transmission fluid in total, using a special power changer that drives out all the old and substitutes new fluid has a positive effect on shift quality IF you use a synthetic fluid such as Mobil brand synthetic fluid as a replacement. There are 10 quarts or so fluid at $4/qt. plus the service charge, but that might be a better investment from what I hear.
Please let me know how this progresses so I can learn and share it with others.
Roland
PS Am I correct that the car is the older style C-body as opposed to the LH body that was introduced that year?