tire ballooning in the rear, but not front...

[What's_nitro?]

Well, I can tell you that the front tires are going backward because you put the front diff in upside-down. Just flip it over so the diff spur gear is on the other side of the diff input pinion. As far as the rear tires ballooning more, with the front tires pushing back, that would amplify the symptoms. Are your rear shocks set up very stiff? That will cause more weight to stay in the front on acceleration and so the rear will slip more. How is the F/R balance of the truck? Are the batteries/motor in the stock locations? (sorry, I'm not the E-maxx pro on here :/ )