Running nose high will cause some minor tire wear but if, in 5K miles you have scrubbed most or all the tread off, I would check toe in and consider that you have a bent axle, possibly tweaked by a high crown road or a rock in a CG. My experience with running nose high on a past 5er or TT hadn't increased tire wear a bit.
Additionally, 18" wheels, and if they are originally from a 3/4-1 ton 8 lug pickup truck will most likely have the incorrect centerline offset backspace, measured in inches, not a few millimeters. Trailers, especially with Dexter axles are usually zero or very close to that number. With this said, I would jack up a corner, pull a wheel and check bearings as well as the backspace of the wheels. This is particularly true if you have Dexter Nevr-Lube hubs.
Good luck and keep us in the loop
Dave W along with my DW, Susan and our poodlepups, Callie & Molly,2011
Ford F250 6.7 CCLB, 5er Hitch Option w/B&W Hitch,,Ride Rite air bags, 2014
Montana High Country 343RL (38')