Get a 2' carpenter's level and check the tire camber (vertical plumb-ness). Should be the same for all wheels. Get a 6' straight edge and check that the outside of the tires are in alignment from front to rear (all should just touch the straight edge). You can do this by pulling a string taut from front to rear as well. A shop that deals with the front axles of semis can re-align, but a replacement axle may be no more expensive. Just depends on the shops in your area.