"Fine until I put power to it" Sounds like Diff to me too.

1. Tweak is perfect ?

2. NO binding in the rear pod ?

3. Diff clean and smooooooth ?

4. Rear wheels spaced exactly the same from the center ?

5. Tires the same diamater ?

6. Front springs the same ?

7. Rear ride height spacers the same on both sides ?

8. Even tire sauce ?

9. Front wheels rubbing at full steering ?

10. Front wheel bearings the same ? (not too tight?)

If not any of them, I give up. It sounds like the steering is coming from the rear, but you never know.

David Root