I have a minor, but annoying problem on long x-country or trans-oceanic flights. After reaching cruise altitude, speed, and course with Auto Pilot set, I accelerate FSX to 16X, as I don't have the time to sit through an 8-hour flight.
At altitudes above 18-20,000 feet I then get strong pitch oscillations as much as + - 2,000 feet, depending on the size and weight of the plane. This happens with all default, freeware, and payware planes that can reach those altitudes, but causes no problems other than annoyance.
My memory is cloudy, but it seems to me that this did not happen with the initial FSX installation, but rather appeared after installing SP-1 or SP-2. I am curious to hear if others have the same problem, and - even better - if anyone knows of a solution. It seems to be a universal problem in the auto pilot mode.