Did read about others that changed to much larger tires and lifted the trucks. Fuel mileage did decrease but there are oh so many factors on the tire/road friction, the lift and air resistance that it is tough to figure.
Other issues involved are calibration of the speedometer which may have an effect on the EVIC operation. Now don't forget the lower gear ratio you will be creating. Actually, for fuel mileage, that would increase it and offset some of the resistance increase.
The answer is ...
If you are like most others that do it, you will spend huge amounts of money for the look and really don't care about a little bit of fuel economy. Maybe that's why I never read an exact report on the mileage issue from those that do it.