Start by checking your wheels first. If you like to rally or have slid into things you have a high chance of bending your wheels. A bent wheel will cause vibrations and also bearing and seal failure. Your wheel is also much easier to bend than an axle. I have bent many a wheel and have yet to bend an axle. To check for a bent rim you can install it on the front of your rig on jackstands and spin it by hand or other similar methods. You will be able see the wheel wobble. After you have verified that your wheels are bent you can replace them and proceed to the next step.
By installing a new rim on the suspected axle with the rig on jack stands you can use the engine to spin the axle slowly to check run-out.
As for a bent housing you will not see a wobble at the wheel.. You will however have a problem with your side and spider gears if you are open diff or you will have alignment problems at the locker...
