Another thing to check, I ran into this on my 94 Intrepid (same car): The ignition switch. These vehicles use a switch that is separate from the lock cylinder and really quite easy to access and replace (remove the column covers, requires, *maybe* a security torx bit). My Intrepid would randomly drop into 2nd and the gauge cluster would go dead. There are separate contacts (apparently) in the switch to provide power to the PCM. Key dance revealed (forget the code number) that was something like "failure on vehicle communication bus". That *sounds* scary, like , OMGWTFBBQ A $200 MODULE IS SCREWED!! but no, it was just one module (powertrain, not engine) dropping out while the ECM was still humming along. It throws a code because "hey, my PCM isn't talking to me anymore" and the transmission is electronically controlled, mechanically designed to default into 2nd gear when the selector is in any forward range and it is not getting input from the PCM.
Anyway, this was literally a $0 fix that had been a MAJOR headache for me as I didn't even replace the ignition switch, all I had to do was clean it. It's been about 10 years since I did this, but IIRC there is a ring shaped bit of plastic that unclips from the cylinder-end of the ignition switch unit, the tabs on mine broke off and there is a spring inside you should take care not to lose, but when mounted, the body of the switch is held firmly against the back of the cylinder so the broken clips aren't even a problem. I opened it up, removed the moving assembly, the contacts are at the bottom, I sprayed WD-40 on them, worked the rotor around a bit, maybe wiped it out and sprayed more in, dunno, but in the end I NEVER had that problem with the vehicle again.
That was turned up after EXTENSIVE internet research as a slight possibility of being the culprit and in my case it was. This vehicle seems to have A LOT of problems with switch contacts. Only one of the door switches is functional, while the other 3 do not light the dome light when the doors are open. There's other switches as well that I have had to clean to bring back functionality. I just think in the 93/94 range Chrysler's suppliers on switches had some quality control issues.
One may be able to test this by seeing if striking the underside of the column, or rocking the key back and forth without shutting the vehicle down, while traveling, causes the problem to occur. It will not spontaneously resolve once the transmission is in limp mode, you must restart the vehicle to clear the error I believe. I actually got into the habit before I diagnosed the issue of popping the selector into neutral (on a straight stretch with sparse traffic, mind you) shutting the engine down, waiting a couple seconds so the engine has completely stopped turning, then re-engaging switch to the start position, allowing the engine to start and then shifting back into drive. You can do this safely without losing much speed and the electronically controlled transaxle will automatically select the proper range based on the input and output shaft speeds which would probably be 3rd.
I hope that helps. Let us know what you find out in any event.