Pete I talked to my friend that runs a Discount Tire about wear. He said the Chevy's due to having the IFS tend to wear the Toyo's more than those of us with the straight axels. I know I have more miles on mine than you and mine are still half half their life left. I know Criag had the Nitto Terra Graplers on his old chevy. He liked the tire but thought they seemed to wear quick.
What tire pressure do you run in the Toyo's? Also rule of thumb to get the most tire life out of any tire is to rotate them every other oil change. If you buy your tires at Discount, I think they come with free rotations too.
Let me know and I will get you in touch with my friend at Discount to get you the best deal when you are ready.