Kiwi,
We had a guy with a MR at our club whos car kept spinning out. Sourced it to the fact that the diff screw came so far out that the drive shaft was hitting it forcing the suspension to stop instead of letting the car lean over. we whipped a few mm off with the dremel and the car was handling fine.
I know when I built my xpro i had to do a bit of dremel work on the wishbones and hubs to get the suspension to move freeley. You are aiming for the wishbones to drop under their own weight without needing a push. To check they are doing this take off the wheels and undo the shock screw on the wishbone. Pull the wishbone up to the top of travel and then let it go. It should drop fairly quickly and shouldn't bind up anywhere when it is dropping. If it is binding take apart and take a bit of material off of the wishbones so that when put together it doesn't rub where it comes in contact with a hub or pivot block. Take a little bit off at a time and try not to take too much off.
I would say that it probably is tyre choice as sosidge has suggested. I run an X-pro on carpet and have been doing for about four months now. On a low grip carpet Schumcaher yellow mini pins all round are ideal, and then high grip carpet Schumacher yellow mini pins on the back and schumcacher staggered ribs on the front are the way to go. I would really suggest asking people at the club what they are using. There is no secret squirrel stuff when it comes to tyres as it is quite difficult to hide what you are running on track.
If you want anymore help just drop us a PM
