After reading all the details you were able to ascertain, I'm struck by the apparent severe lack of maintenance...if the K&N filter was that dirty, the tire wear was really apparent, there was evidence of the tires rubbing, the rear axle fluid leaking, the pinion shaft seal, ball joints, diff cover gasket, etc.......sounds like the PO may have really rode it hard & put it away wet!

I certainly can't speak for all the forum members, but I'd never let SO MANY serious issues go unaddressed, it just makes me feel the PO has been really REALLY hard on the truck and it's been neglected. Again, I'd run away, but maybe the info you can get after the alignment will help.

just my .02 cents!