Optimum Tire Size for my 95 4runner

Bought the 4runner used a few years ago and it had BFGoodrich size 31x10.50R15LT on it. I figured these were larger than normal, and probably the source of my lower-than-I-would-like power (3.0L V6 Manual), and not that great of gas mileage. Checking the plate inside the door, it lists P225/75 R15 as the stock tire. The speedometer seems to be correct, so I don't know if they recalibrated it when they put on the larger tires. I need to replace the tires before this winter, so I am trying to work out what size to get (and make).

I asked a Toyota mechanic about it, and he said around 1995 the plate on the door was actually wrong, and there is a reasonable chance that the 4runner came stock with the 31inch tires???

I live in the Northern Rocky Mountains, so apart from harsh winter conditions, I do find myself crawling around rough roads fairly often during the summer. I do like the looks of the large tires, but I wonder how much more power I would regain if I went to the smaller stock tires? From reading this forum, it appears the 3.0L is simply too small. How about fuel economy?

I am open for any suggestions on a tire make and brand as well. I am not crawling around on rocks down at Moab or anything, but I am also not city driving either. Majority of the time it is on pavement, but on the weekends I am in the mountains. It is my only means of transport, so I do do some 200 - 400 mile drives on the interstate occasionally as well.

TIA - Raoul

Stock tires are P225/75R15

I know that some of the V-6's did come with 31's from the factory. At least when I bought a '94 brand new it did, as did a few of the others on the lot. It had the 3.0 V6 and was an xtra-cab SR5. There were also some on the lot that had the 225's. So it appears to me that they outfitted them with both sizes.