Tire Blowout problems of the 2004 Ford Excursion

I purchased a set of 4 spector advanta a/t size lt265/75 r16 tires for my 2004 Ford Excursion from les schwab in meridian idaho on 15 may 2008. I noticed that at highway speed the front of the vehicle would shake a bit. Les schwab checked the balance, alignment, etc. But noted nothing wrong. Since I use my vehicle for local travel and to tow my travel trailer I don't travel at high speeds very often. On 25 November, while traveling with my family from boise idaho to las vegas nevada we experienced a catastrophic tire failure in the left rear. The tire disintegrated while traveling on a newly resurfaced road at approximately 70 mph. The vehicle sustained approximately $2000 in damage from the shredded tire. Upon return to boise les schwab replaced the blown tire with the same brand. I pursued a claim with the tire manufacturer but they denied it, as did the dealer les schwab. On August 23 2009 we experienced another tire blowout, left rear, while returning from a camping trip. We were towing our travel trailer at approximately 50 mph when the tire failed. I returned to les schwab and told them that 2 failures was beyond coincidence and that I wanted them to replace the tires as they seemed defective. The store manager agreed and tried to work with the tire manufacturer and les schwab to get the tires replaced with another brand. Everyone refused but the manager did replace the blown tire with a used tire from a different manufacture. I subsequently transferred to las vegas and commute to boise on the weekends. On 25 October I experienced another catastrophic tire failure, this time the right front. I was traveling at the posted highway speed 75 mph and almost flipped the vehicle when I ran down the shoulder into the field. The tire tread had completely separated from the steel belts and was strewn about the road.