I'm sure you do but I'm still going to ask, Do you have fsuipc installed?
One day I was doing something tweaking maybe fsx Which I'm always doing can't remember exactly what and took fsuipc out of fsx and forgot about it. Then one day I fired up CS 757 taxied to the active took off climbed to 2000ft agl engaged the auto pilot and that thing started going wild like it had a mind of it's own. I was lost at what the problem could be and then I remembered fsuipc. Once I reinstalled Fsuipc all was normal again. I hope this helps and is the solution to your problem, If not I'm sure someone will come up with something. After all this is why we come here to share experiences and to help each other out.