This is weird!!!
I was recently looking at the rear end of my 2008 Tacoma Access Cab SR5 (2.7L 4 cyl) and comparing the amount that my (new!) X-Runner wheels stuck out from the sheetmetal of my rear fenders. As I looked at the passenger side, the outermost edge of the tire is about 1/4 inch OUTSIDE the sheetmetal...but when I looked at the driver side - the outermost edge of the tire is inboard of the same reference point by about 1/2-3/4 inch! Basically, it looks like when they attached the rear axle to the leaf springs, they mounted it ~1 inch off of center pushed toward the passenger side!
When I had the original 15" stock steel wheels on, it probably wasn't obvious because they were so far inboard of the fender wells...but with my new X-Runner wheels being so wide, they are easy to compare to a common reference point.
Can you go check your truck and see if you note this on your vehicle? It seems that this would cause an alignment (and early wear) issue due to inaccurate tracking front to rear.
Thanks for letting me know what you find BEFORE I take it to the dealer.