What is causing my rear tires to wear prematurely?

What is your question?

We bought our 2008 Sequoia in May 2009 (no production of this vehicle in '09) I just purchased my 7th set of tires as this truck eats them for breakfast, lunch and dinner. We have had the rear aligned multiple times with no improvement. Is it possible that the weight of this vehicle is to much for this size tire? When pulling into a parking spot the rear tends to slide sideways if I don't crawl into a parking space - that has been a problem since first week of owning it. I love everything else about this truck but unfortunately this problem will prevent me from ever buying another.