Thanks to all for the replies. Going by the guidelines on the Michelin site, the tires are still safe to operate. Two days ago when I checked them, and I check them frequently was the first time I had ever seen any cracks. I will continue to monitor them and when the exceed the depth for safe operations I will replace them............but I don't think they'll be Michelin's. I don't see the advantage in paying nearly twice as much for tires and they still crack in about 5-6 years. The savings will $$$ will put a lot of diesel in the tank.
Thanks again, and Merry Christmas to all !!
Brian