differences in mpg when towing

Why am I seeing a difference in mpg on the way there we got 9.2 mpg on the way home we got 11.7 mpg The only 2 real differnce is brand of gas and we drove through some rain on the way. I set the cruise at 65 mph and locked out sixth gear once we got into Missouri both ways much more hilly than flat illinos. Used the exact same route yes I have the eco boost with max tow haul 4x4. I am very happy with our tv just curious about the change in mpg. Oh used 89 all the time not just towing