tommyc3 ... I'm unsure why the change of belt would alter the way the drive wheels are operating. Are you sure that both wheels are pulling, albeit one more than the other? Is it possible that one is not powered at all? The power coming from the transmission should be the same to both wheels.
First, make sure that you are getting ANY power to one wheel. If one is not driving at all, then something is probably wrong in the key/gear assembly at the end of the outboard shaft. Did you take one wheel (both wheels? off? There was no need for belt replacement, but you may have done so anyway for other reasons.