I went to the mechanics house this morning. As soon as he put in the other computer, it started shifting perfectly.
So he must have been right - that the computer D found for me was for a stickshift instead of an automatic.
He took the old computer as partial trade for the new one, and just asked for $100.
So, when all was said and done the idjit who decided they needed my car's computer more than I did, ended up costing me $140 in actual cash, 4 hours lost work time, and an extra 60 miles of driving time.
Please, please, please Murphy stay away from me! You've spent enough time messing with me and my car!