Wandell can answer! lol
#1
#2
If your truck is a 4x2, the 265/70-17 BFG's should work fine. If you have a 4x4, I'd go with 285/70-17's. The added height will affect your milage slightly. It will also throw off your speedometer/odometer slightly which means you will be traveling faster than the speedo shows. It will also mean you are traveling farther than your odometer shows.
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#4
The Mud T/A is a great looking tire but "BEWARE"... I had them and just got rid of them. I heard most people only get about 35-40k miles out of these and at first I thought what are they doing wrong. Now I know it's not because they wore out, it's because you can't stand them after that. My tires got to about 40-45k before they just went to crap. They were about to beat my truck to death literally. Bad part is I had only used about 60% of the tread. Always kept the front end aligned and cross rotated every 5k. Doesn't matter. It was sooo bad we went on vacation and drove from Sacramento to Seattle. We don't drive the truck alot together around home so it was quite the experience for the wife. Anyways, long story short, it was sooo bad on the way home my wife made me stop in Portland and buy new tires. Found an America's tire (I've been dealing with for years) and bought a set of Nitto Terra Grapplers. All I can say is AMAZING TIRE.