The only difference between your truck and mine is I got the Max Tow. Your TT has the same dry weight (roughly) as mine. You will be fine.
There are many variables on MPG. Downhill with a tail wind vs uphill with a head wind for example. The single biggest factor is how heavy your foot is on the accelerator. We tow with TOW/HAUL on and the cruise control set at 62.
While I haven't done the numbers with my current rig, the 32' Class C I traded off last April got 9 MPG at 62 MPH and 6 MPG at 72 MPH. That was a 16% increase in speed at a cost of a 33% decrease in MPG. (That was a test I only did once.)