I'm guessing this is a .40 size plane, and also with the Saito .82 you're swinging a 14 or 15 inch propeller. I would guess that it's mostly P factor. After you got it all trimmed out, did it try to roll right if you suddenly let off the throttle? A lot of the 3D guys will overpower a plane so they can swing a massive prop that will allow them to hover at just more than idle. The difference is that 3D planes have much more wing area, and the P factor isn't as pronounced as it would be on a sport plane. Try a smaller prop ... maybe a 13X8 or 13X6 and see if that helps. If not, it's probably either tail feathers or latteral ballance.