I've had the vehicle back at the car lot for the last few days, and the owner swore it was fine, says he's not seeing the problem I reported. I picked it up today, and literally 5 minutes on the freeway (again!) the SES light came on. I turned around and went back. Their reader showed the same code, so he test drove it. Upon his return, he acknowledged the hard shift and believes it's because either the fluid was overfilled or had the wrong kind of fluid. He says leave it with him a few more days and he'll fix it.
The neighbors across the street from us own and run their own race cars, fixing them up in their garage themselves. On a hunch, I just walked over and explained what was happening. All three said it was either the converter or front transmission pump. Either way, I'm looking at at least $1000 worth of further repairs.
I'm inclined to believe them, even if they've never driven it, because they rebuild all of their own transmissions, and would have no reason to lie to me. So I guess what I'm wanting to know is if I should put it in the shop, again, and hope that is all that is wrong with it, or could I drive it and just ignore the hard shift in the lower gears?