I'm shopping around for new tires for my car right now and it got me thinking about what tires I will be putting on my truck in the near future. I have a stock 2005 Silverado 1500 ex cab. It is 4x4 with the Z71 package and 4.10 gears. I plan on leveling it and getting a set of A/T's or possibly moderate M/T's. I'm perfectly fine with running stock size tires and just leveling out the truck but, like a lot of 4x4 truck owners, I would like to run 33"s. I assume most 285's would fit fine with just an extra 1" tall block in the rear and a torsion key kit set to 2.5-3" in the front, or whatever it takes to level it and maybe keep a slight rake. The thing I'm really curios about though is how 33" tires will change the performance (if even noticeable) of my truck given my gearing...theoretically it would improve mpg's as well as lose a little towing power. While I seriously doubt either impact would be significant enough to result in making a case that either size is more or less efficient I'd like to hear some opinions or facts. On a side note, is it typical or possible to get your computer programed to the new tire size for things like transmission shift points? And if so, is it recommended? TIA.