Tire Size Recommendation

So, I have a 2000 Tacoma Prerunner 2x4. It currently has 265/75/R15 bald tires on it. I'm looking to replace them in the next month. Any recommendations on tire sizes? I already get 15 mpg everywhere and its a slow V6. Would a different tire size make any noticeable difference in my mileage or acceleration? Best I can tell the truck has 4.10 gearing if that helps.

Has anyone actually hit the 21 mpg highway with this truck or what's the best gas mileage you get? I've had as low as 14 and its hit close to 18 a time or two.

 

I just put 31x10.5/R15 on my prerunner 4x2 2.7L. Looks great.

 

I have a 2004 DC with 265/75/16's and consistently get 20 mpg on the highway.