Tire Pressure Light On problems of the 2004 Toyota Sienna

I have concern with tires and low pressure light illumination . I had 15k service at dealer on July 22, 2006 with 15,423 mileage and they said the tire wear pattern for four tires is ok. Also dealer adjusted, inspected and rotated the tires at that time. But during 2,000 miles drives after service, the low pressure light was keep coming on even though I kept the proper pressure in them. So I went to firestone for check up and they informed me that I need new rear tires. I went to costco for 2nd opinion on November 22, 2006 with 17,647 mileages and they informed me that I need two new rear tires due to worn out. I was pretty upset at unusual rapid worn out right after manufacturers recommended 15k service. I send the letters to Toyota but they don't even send a reply letter.

1. Run-flat tires get flat significantly more often than regular tires. 2. The low pressure light does not always go on when the tire is flat and off when the tire is not flat. 3. The tires get worn out after around 12k highway miles and are expensive to replace. 4. Most of the shops do not have the equipment to handle the tires. Specialized places have to wait long to order the tires.

I purchased a 2004 Sienna brand new in 2004. Toyota engineered the 2004 Toyota Sienna w/ dunlop run flat tires. As such they designed no space for a spare or a jack. Including 4 tires that were replaced as part of a recall I have replaced a total of 13 tires in 6 years. These tires cost almost $300 to replace. The low tire pressure warning light has never lit up, Toyota tested it and stated it works but have no idea why it does not light up when the tire goes flat. Toyota takes no responsibility for their design choice in any way. I have requested everything from partial reimbursement to a full set of regular tires with a spare and a jack. All requests have been refused.