The axle that connects the diff to the wheel is either a "dogbone" - (looks like a bone when you remove it), or some type of CVD or "constant velocity driveshaft". If you still have "drive cups" on both the diff and the wheel, where the axle sits, then it is a dogbone, as CVD's replace the dogbone and the drive cup on the wheel side with one unit.

So apart from the axle the car is good to go, right?

And another thing, make sure you loktite all of the grub screws unless they WILL come loose again. You should be able to get some loktite from the hobby shop, and make sure you get the medium strength stuff, the high strength will prevent you from removing anything when you actuall need to remove it.

Glad you found the source of the problems, it is usually something as simple as a missing screw which causes all the problems - (my car was acting all wierd a while ago, it keps spinning out under acceleration or braking. I discovered that it had changed to 3 wheel drive as a grub screw had come loose)