Mileage should increase with higher temps I think. But it probably has more to do with the fuel blends of the seasons.

In the OP's case, the 35's are what's killing it.

 

I have the same truck with a fresh motor, new injectors, new cops, same tires, same CAI and I'm driving around in the 105-109 temps everyday here in Texas getting 10.5 MPG just like the OP. If I reset and run down the highway only at 70MPH I get 18 MPG. I think it's the tires and the heat and my heavy right foot unless my neighbor has cloned my garage door opener and is stealing my gas at night.