Just came back to Missouri over this same pass through the Ike tunnel. No issues at all with the Tundra. We are only pulling a 23FB though.
I kept it in S 5 almost all the time, and used the cruise control. My back is acting up, and using the cruise helped my comfort, quite a bit.
We went out on 24 through Colo Springs, then over to Buena Vista and up to Leadville. I was getting over 10 mpg with some tanks better than others. I try to set it at 67 and ignore it, but I did get going a little faster from time to time depending on traffic. Not sure if the racks and kayak cut into our mpg or not.