Weird problem...

That tire looks like it was rubbing on something. In anycase probably would not cause the drifting trailer. Looks like some one has dragged the trailer over a few curbs getting into deliverys.

 

Sharp metal edge.

 

Check the fifth wheel plate that it has grease/lube. If it’s dry, you could get what you’re explaining.

 

Oh, this isn't about pretzel rods again, is it,,but I agree^^^, a dry 5th wheel does all kinds of things, but seems to me, the tire wear is indicating a severe alignment issue. Loose wheel bearings may be more noticeable under load, tire pressure maybe?

 

Those are the Michelin XDA 5+ tires, not retreads. And when they’re new they have 30/32 tread which would absolutely make the truck feel like the back end is sliding out from under you. It will probably feel this way for a couple weeks at least. And the reason the tread looks the way it does is because they used a truing machine on them.

Edit: I also see your tires are 11r22.5. Tall sidewalls with nearly an inch of tread on new tires will make the back end feel loose.

 

It's my truck it took 4 hours of time. Plus getting to mechanic and having them order 5th wheel ect....

 

Adjust your mirrors and see if that helps.