I attempted a "Copilot" controlled flight in the B777 this afternoon and experienced some wild gyrations trying to maintain the set cruise altitude of FL410. I don't think the plane was ever at exactly FL410 for more than 2 seconds. It was either climbing or descend at up to 2,500 FPM constantly. I was getting Altitude Warnings up the Kazoo and an occasional AP disconnect. Heading Hold was right on the money. Climb to altitude worked just fine. Lost the flight just over half way. Bummer.
I did notice the rigging and trim may be off a bit. An external side view has a pronounce nose up attitude when it should be more or less level. I was indicating Mach 0.89 - 0.90, 79% thrust at FL410.