i will back up those whom said your ball mount on your hitch is too low, causing the tongue of the trailer to point down. when this happens, the front axle carries the majority of the weight. when you corner, the front tires will be the pivot point of the trailer, which will cause the back axle (and consequently the back tires) to slide, hence the premature rear tire wear. it is kind of counter intuitive. there is a simple solution:
i just picked up one of these for my truck. 10k max tow weight and 1k max tongue weight (for those of us that keep lead in the bow!). and it folds out of the way to hide itself from your shins! it is pricey, but it is the last hitch you will ever buy. i tow three different trailers with three different tow heights, and it adjusts for all of them. i opted for the three ball option just so i would always have the right sized ball. the company's web site is www.turnoverball.com
, but as always, ebay is your friend!