Just a thought: perhaps the breaks on one of your trailers are not engaging correctly causing the excessive wear.
on my list to check when it comes out of the garage. I haul a lot of machinery/etc so could be an issue too. I changed them maybe a year after I got the truck and then a year later they were crap. I changed out all 4 because 1 had pretty much imploded and was not very impressed with the quality. I'm at close to a year now on the new pads but haven't checked them lately. My ex has an 04 xl and has had similar issues. Good news is I can change the pads in 15 extra minutes on top of a rotation. Easiest pad change I've ever dealt with.