Chrysler Repair: 1994 grand Cherokee Laredo, snap on solus, grand cherokee laredo

Question
Hi, I have a 1994 Grand Cherokee Laredo with a 42re all time 4X4. It was shifting late as high as 2800 from 1-2 and 3500 2-3 and NO 3-4. I slackened the TVP cable by almost half it's adjustment to get it to shift better(1-2 2500 2-3 2800# but still no 3-4. I hooked up a Snap-On Solus scanner to the tranny and went for a drive on the interstate the TCC solenoid was off and the O/D solenoid was off unless i pressed the O/D off switch in the jeep, then the TCC and O/D solenoids were on. There are NO codes
set my cone concern is that the output shaft speed sensor was Reading no higher than 12rpm but did rise and fall with the vehicle speed. I am running out of Ideas but do not just want to throw new parts at it, I am aware that my fluid needs to be changed it is old and thin and the temp sensor was reading 236 F at one point (I know OD will not go on in a perceived overheat situation) I hope you can help me, if you need more info please let me know. Thank you =Paul

Answer
Hi Paul,
I don't have Jeep manuals but I wonder if your scanner was capable of reading the trans codes? Your vehicle is OBD-I system, and to read the trans codes you need something like a Chrysler DRB-II code reader with the adapter to plug into the Jeep socket under the dash. You have to specifically seek a readout of the trans controller as the code numbers overlap for the engine and transmission.  I am not familiar with the Snap-on Solus model, but it would be surprising if there weren't trans codes related to the problems you describe. I only have manuals for the Chrysler car lines in those years, but the electronic transaxles also used 2-digit fault code numbers in the same numeric range as for the engine so if you could get any such   trans-specific numbers I suspect they will be identical to the ones I have for the Chrysler 42 series trans. The output speed sensor sounds way off (was that 12 rpm?) and that will of course set codes and certainly mess up shifting. Replacing the output sensor might be worth a try given that it is under $100 and you can do it yourself.
Roland
PS I don't claim to be a Jeep expert. But if you would 'rate' my answer and where you see the question about 'volunteer of the month' consider giving me a 'yes' that would be appreciated.