I was about to post a reply to this topic that I know I saw,but it seems to have vanished into cyberspace.Well,for whoever`s interested,here`s what Ive found:Autopilot is almost useless above FL45,exept for heading maintenence.The plane has a mind of its own,and at full AB will keep climbing,steadily increasing angle of attack until it stalls.What you MUST do is climb to target altitude MANUALLY.Once there,engage ATL HOLD,and "finesse" throttle/elevator trim.Once aircraft is reasonably stable,expect a1000FT+/- porpoise.Ive found 400KTS is optimal at altitude for best performance.This aircraft is not a Cessna ,dont expect to set autopilot and walk away.Even once youve achived level flight at designated altitude,manual control inputs/corrections may be needed.I just did this today:Beal AFB to Damascus,and I thought I had AC stable at FL52,so I left program run while I went to work,only to come home and find I`d munched the ice somewhere above the arctic circle.This is a good plane,and it WILL go to the FS2K2 limit of FL100-Ive done it!It just takes alot of "want to"Hey,dont let HABU kick your can-strap it on,not vice versa!