[neallewis]

Mid/rear motor isn't the issue. Mid motor works very well in the lowest of traction tracks. The issue is the unloaded wheel is spinning up. If your tyres are ballooning, then I'd say the driver is giving it too much throttle when the car isn't straightened up. Are you running the right tyres for the track? Same as the local top guys. Suspension setup, what do you have set. Fill out a setup sheet so we can see. Check your rear shocks are not pressurising. I noticed this with the plastic shock tops. When this happened, the car became undrivable. Bleed.
Diff. I run a ball diff and would on low traction, as I've experience in setting it right. I've not yet messed with the gear diff, but again the oil may be wrong.
Slipper. Is it too tight and not slipping?
ESC. Is the initial acceleration or punch to harsh?
Give us a bit more info on your setup and we'll suggest some changes to try.