Which stores say they can't pull TCM codes? A pocket scanner, aka, code reader should be able to pull up any P07XX code, if it's there. Keep in mind there may be pending codes lurking that the parts stores puke don't, or can't, look for.

Check to see if their tool rental has a real scanner you can use to check for set and pending codes.

You could stumble around for days blindly trying to find a fault in the TCM circuits. Codes, then trouble shoot using a digital Volt/Ohmmeter and wiring diagrams.

 

If you want, you can read the resistance of the solenoids in the trans.

Go to this thread (which is not your situation) and refer to the TCM connector pinout in post #3, and do the resistance checks stated in post #7.

 

Turned out to be a fuse. Passenger kick panel. One of the larger ones up top.