Ron W.,
Try this link. Grate Temperature If it does not work then do a search on this site for "grate temperature", scroll down and there is a topic "Temperature Differential Between the Lid and Cooking Grate". I really have not figured out how to post with a link. Hope this help. Rodgers.
Ron,
There is normally about a 10-15 degree temp difference between the dome temp and the top grate temp. And about 5-10 degree difference from the top grate to the bottom grate.
i think it also depends on how you have the WSM loaded because I did 3 butts in one and two in the other and must have had more than a 10 -15 degree difference between the top and bottom see my other post I'm starting regarding this.
I usually find the top grate avgs 15 below the temp in the vent.