Ed,

another thought. I'd make sure your servos and linkages are rock solid. At that speed you might be getting some flutter issues if they aren't. Also, one of your servos might be drifting under load causing the model to roll. Either the right aileron is dropping or the left is rising. I suspect the latter.

While at it, check your elevator too. I'd also put your rudder on P-P if it's not. The rolling tendency might be coming from rudder.

Say, what crank rpm and prop are you turning on the P80?

David