Mike, I have the same tires on my 5er and "rule of thumb" is to have them replaced after 5 yrs. There is a Wingfoot Dealership off I40 at the Candler exit.....At 6 yrs, you're really pushing your luck..When I replaced mine, they too looked brand new. They are an expensive tire and when it's time for me to replace mine, if the GY G614's haven't dropped in price, I may look at the Sailun tire that has been much talked about on these forums....A China made tire, albeit, a high quality tire, that I will look at when the time comes and possibly purchase instead of the GY G614's..
Jim