There's a good chance the auger is bent, most likely at the point near where it bolts to the output shaft on your gearbox. I would unbolt the auger, and go find a SMOOTH, FLAT, LEVEL concrete pad and roll the auger and see what it does. Pay close attention to the end that bolts to the gearbox while you roll it. If it's warped, it will show itself by the "wobbly" motion. If the auger seems to be true, and doesn't wobble on the pad, then check your gearbox. The problem could be the output shaft is bent, or possibly the PTO shaft is bent. You should be able to start up the tractor, engage the PTO, and spin the gearbox. If there is still a wobble to it, it should still show itself even with the auger not attached. It just won't be as pronounced. Good luck.