[JIMs70GMC]

zach, I'm running 33-12.5 super swampers (about 34" tall). It's real easy to add the leaf it will make it stiffer but you might not be able to tell the difference. When you remove the u-bolts to add the block, you take a big c-clamp and clamp the leaves and remove the bolt through the center of the spring pack. Then you slowly remove the clamp and the leaves will come apart and put the new leaf (usually on the bottom(above the overload)) and put a new bolt in through the center(comes w/ new leaves) and pull the leaves back together. Put the block and install new u-bolts.
I have 15" rims on the GMC fit because of the drums up front, on the Chevy I have 16.5" rims. I believe the biggest thing is the 16" and 16.5" have stiffer sidewalls and require higher air pressures. What tires were you look at? I'd suggest going to the manufacturers web site and look at the specs on the tires.

Also i went with the 33" tsl because of the higher load rating as a 15" tire. If I had it to do over I would have went with the 16.5" rims and tires. (I don't rock crawl and have no need to air down my tires)