I would suspect a few things as a fault of your increased tire wear: The quality of the tires. Are they Chinese or a name brand? Are they being run at or over their rated load capacity?

Before you consider an improper axle alignment, look at how the tires are wearing. If the thread is worn on the same side of the tires on one axle, then an axle alignment may be a problem. Were they scuffed and wearing unevenly on the one side, when you took your trailer to a wheel alignment/ frame alignment shop for a check?

If each of the tires are worn in the center of the thread, they are over inflated. If all the tires are worn on the outside of the thread, they are under inflated. 5 psi is not enough under inflation to cause premature wear unless the tires are continuously used at their maximum load rating which is dangerous to do. You need to have an axle / tire rating that exceeds your total load factor to give you a reserve capacity.

On each tire is a maximum load rating stamped on the side wall. Multiply this by four and you will have the tires' max carrying capacities. Add up all your weights and subtract 25%. You will then have your actual loads. How do they measure up to each other? More capacity, less or even? The best scenario is to have more capacity. If you have less, you will encounter premature tire wear.

If the alignment shop can verify a misaligned axle, you will have to present this information to your dealer so that it can be repaired. It should be a warranty item. Don't let the dealer blow you off while blaming  under inflated tires as being the problem.

Gard