NC-Expy, it is going to be close. For normal driving, you shouldn't have any issues. But, like was mentioned, under full flex (which is what I base everything on), you may have a little bit of rubbing in 2 places. The more obvious one is on the inside back edge of the front wheel wells. That is the first place (after trimming the valance) that if you are going to have rubbing, will be there. I know an easy mod to remove this problem and is only about a $5 mod to do. The big question is whether you are willing to apply a 3 pound hammer to the body of the truck. The other place I see you having a problem (due to the width of your rims is the top edge of the rear wheel wells. Due to running 18x9 rims,your tires are going to stick out about a half inch more than someone running 18x8 rims. In the case of my 37x12.5's on 8" rims, my tires just barely tuck under the body for clearance (I can't fit my finger between the body and the tire-got pictures to show).
Now, the easy fix to all of this is a 3" body lift. THen you are golden all the way around. If you don't plan on twisting the truck up, then you are good too. But, if you plan on taking it out 4x4ing, other work is going to be needed.
As for backspacing, you can determine it yourself. All you have to do is to pull a wheel off and put it face down on the ground. Now, using a straight edge, run it from the metal part of the rim where it meets the tire to the exact opposite side of the rim. Now, using a ruler, measure straight down from the bottom edge of the straight edge to the back side of the rim (where the studs go through). This is your backspacing. It should be either 4.5" or 4.75". In your case, 4.75 is going to be better for you as it will help tuck the tires a little bit and ease your chances for tire rubbing.
