RE: Plane rolls at different rates left and right?
Assuming an engine with standard rotation, torque would roll you faster to the left, not the right, so I doubt it is engine torque. There might be something funny going on with slipstream. You can check this by repropping and/or flying the rolls at a different speed. But my gut reaction is the engine is not the problem unless you have too much side thrust.
As others have posted, an Extra shouldn't need much if any aileron diff. I'd suggest taking all the diff out. Double check alignment of airframe, wing, stab, rudder, engine, etc. Be sure you are not carrying rudder trim, wing isn't warped, etc. Check hinge gaps, seal if necessary. Check that not only your total throw left/right is symmetrical, but that it is symmetrical across the sticks. I.E., your endpoints match, now check 1/2 stick throw. Does that match left/right?
Once satisfied with airframe and throws, fly and retrim if necessary. Land and check where your trims are set. If you had to put a lot of aileron trim in and the ailerons are not level with the trailing edge of the wing, something is still out of wack, i.e. warped wing, etc. Once happy with the trim you carry, very carefully perform rolls taking care not to impart any other stick movement, i.e. elevator, etc. I have often seen rolling issue do to the pilot pushing/pulling elevator as they roll. Once everything is set properly, any yaw from roll should be so small it will be difficult to detect.
Cheers