I'll reinstall and see if it helps. I'm wondering, could the joystick contribute to such behavior? I keep my joystick calibrated, but something weird is going on with it, because when I slew, the airplane isn't still. But keep in mind the autopilot doesn't go off, it just violently flips out.

Thanks for the info about the autopilot failure, Blover, but it's hard to find the right page when you're barrel rolling in a dive!  ;D

UPDATE: I reinstalled per Mark's suggestion. I also examined my joystick. I have a Logitech 3D which has served me faithfully, but is really sloppy now. I found that the sensitivity was at the max, and null zone at the minimum. I using slew to experiment with different settings, I finally arrived at settings that were less sensitive. I don't know if that could have anything to do with my problem, but anyway, it is a lot better this way.

So I had a wonderful scenic flight up Central America from Bogota, Columbia to Mexico City, Mexico. The 757 performed perfectly (except for the no T/D issue). So whatever the issue was, apparently it's fixed.