I too am having the same issue....for the past three days I have been trying to fly PANC-RJBB...I follow the checklist and procedures all the way up to cruise alt to the letter....then I fly through about the first hour on 1x and everything is fine, then I switch to 1/2x and go to bed....when I awake in the morning, the queen has made about 30-40 circles over various waypoints, and has also dropped altitude and once was flying at over 500kts....there is another post with someone with similar issues regarding the LNAV, but so far I haven't found any solutions to this(other than flying at 1x and changing the setting to pause at TOD to prevent from running out of fuel)My system is Dell XPS 420, Pentium Quad Core 3.25Ghz, 4GB RAM, GeForce 8800 GTX.-Aaron