[wingnut60]

That is a much-discussed subject, and I do not know of any definitive answer. I have heard/seen 3-4-5-6+ years talked about, and also have heard from several on forums of getting more years and less. Tire compounds, UV exposure and many other factors come into play. I intend to run my Michelins until the tread becomes a factor, or I begin having flats or a blowout--at that time I will re-evaluate. Currently, I have about 16-18000 miles on them and they all have even wear and good tread depth. Minor sidewall checking that began the first year that seems to be normal on Michelins.
I plan on a trip to AK next year that may cause me to rethink as to replacing them, but my truck will also need tires at that time so it will be a large dent in my budget--10 tires @ $300 each--yikes.
Joe