how much mileage will I lose?

I'm thinking of going with a 2" leveling kit, Dick Cepek DC2's (20 lbs apiece) and 265/75/r16 Kuhmo Road Venture SAT KL61 load c (44 lbs apiece). I know that my MPG will be affected, but how much will it drop? If I'm correct the stock SR5 rims are 26 lbs each and the stock Dunlop tires are 32 lbs apiece so will I really be affected that much?

BTW I get in the neighborhood of 22-23 MPG consistently.

 

It's actually a simple formula, though time consuming to expalin. Based on what you said, you will loose 2.67 MPG city and 1.14 MPG on the freeway.