We have the 2010 Sequoia Ltd 4x4. We get about 15mpg on the average, not towing, but also keep in mind I live at about 8k ft so navigating hills is a common occurrence.
Important note: The 2010 Sequoia has a pretty high tow rating but the payload is not so great. There is no way I would ever tow anything even close to our Sequoia's max tow rating and payload would be eaten up far before the max tow rating was ever reached.
Also, keep in mind when the 2011 Sequoia came out, there were virtually no significant changes from the 2010 model but the max tow rating was significantly decreased when Toyota adopted the newer SAE standard. With our Sequoia and my family of 4, I would tow a TT that maxed out loaded at 6500#. Since my TT weighs more than that and I also load a 650# ATV in the bed of my truck, I have a 1 ton and don't use the Sequoia to tow our TT any longer. BTW, my 1 ton was bought well before any thoughts of owning an ATV...to tow our TT.