The issue cleared without my having to tear into the transmission. As I figured things out and ordered parts, I continued to drive the car. I even took it on I estimate a 1500 mile road trip as it has been so reliable and economical despite the seeming limp mode. About 300 miles from home the battery quit charging and the car eventually had to be towed to a shop and given the distance from home and circumstance, I just let them deal with it and largely stayed out of it. They diagnosed a bad alternator (and the one in there had been only 5 months old and has since been refunded under warranty) and replaced it as well as a 10 amp fuse. When I got into the car and saw the DTC 56 issue cleared I was ecstatic despite the mechanic and hotel bill.. it being fixed basically made the whole thing worth it. I have also replaced several sensors I probably wouldn't have otherwise touched as well as the ECM with good hard to source parts, and now that the faulty alternator has been removed and replaced; the car is running and driving more terrific than ever! All it really 'needs' now is rear wheel hub bearings removed and replaced and the parking brake sorted; I guess I would also do the rear brakes then too since I have parts on hand for it.