Would appreciate the groups thoughts on tandem axle issue

With that low of miles I think it's a case of a poorly welded spindle. Seems like whom ever was welding the spindle on screwed up and welded it on crooked.
It normally takes a while for an over loaded axle to bend enough to get bad tire wear. If you only towed it 140 miles and then figure in how far it was from the factory to your dealer that would be the total miles. Being delivered from the factory it should've been empty so overloading wouldn't be an issue.