Help with tires

Just got a new 09 Tacoma Crew Cab V6, 4x4. It came with the 245/75/R16 tires on 7" steel wheels. The tires are junk and I want to replace them with 265/75/R16s and use my steel rims. I have had this size tire on other Toyotas and am wondering if I will experience any problems with rim width, loss of mileage or loss of power. Some models of this truck come with the 265s on 7.5" rims and I would like to know if there are gear ratio changes from model to model to adjust to the change in tire diameter. The speedo is off by about 2 mph (fast) and I think the larger tire size would just about make that up. By the way, when a speedo is off by 2 mph (or 2%) you lose about 720 miles off your warranty. I checked mine with a gps over 300 miles.