[thstone]

The vehicle response to running one new and one old tire in the rear is somewhat unpredictable. After several thousand miles, this may have caused the fronts to wear differently causing the pull. Flipping the fronts may have brought back balance - for the time being.

At this point, running the front tires backwards only introduces more unknowns which can't be easily sorted out.

You need to get back to a stable tire configuration if you want to be able to diagnose and ultimately solve the problem. Any decent mechanic will tell you to first replace all four tires, second get the tires balanced, and third, get a good alignment.

Odds are that your problem will be solved with this regimen. If not, then a bent wheel or suspension component is the next logical place to investigate.