Towing and tire size?

[KLH]

Here is my question, I have 97 Ford F 150 4.6l with the Off Road Package, it has P265 17 tires and a 3.55 ratio rear end. At times it seems to struggle when towing. I was wondering if going to smaller diameter tire 255 or 245 16 would give a increase in power when towing? The literture says to decrease your towing weight by 500# with the Off Road Package, so natually you are changing the rear end ratio with the tire diameter, I dont know why ford does not offer a different ratio with bigger tires?any thoughts would be greatly appreciated. Also any one interested in swapping P255/245 16 tires and wheels with 265 17.

thanks KLH