New tires for my 99 Suburban:Std or Upsize

I just bought a 99 Suburban 4x4 and it needs new tires. The OEM size is 245/75R16, but it has 265/75R16 on it right now. The rear axle ratio is 3.42. Is there any advantage to remaining with the oversize tires or should I go back to the OEM size. I've had dealers tell me I'll get better fuel economy with the larger tires (due to their larger diameter) and another tell me the vehicle was engineered for the 245's and I'll get better mileage if I go back to the original component size. The fuel economy is only 15 mpg at present so anything I can do to improve it is welcome. As I occassionally tow a heavy trailer I was looking at the Michelin X Radial LT tire, a load range E, 10 ply tire which is available in both sizes. Any knowledge or experience you can share is much appreciated.

I have the same truck with the original size tires and just got back from a long trip. I was getting over 18mpg. I will replace mine with the stock size as they seem to work well.

Let me know what you go with and wether it makes a diff. I am in need of some new tires also and dont know if ill be sticking with the 265s or going back down to the 245s