[TheTedP]

When looking for new wheels and tires for a 2005 CrewXE 4wd with a leveling kit, what is the largest wheel/tire combo (staying with 17 or 18 inch) I could get WITHOUT modifying anything?

 

[NorCal 4x4]

When looking for new wheels and tires for a 2005 CrewXE 4wd with a leveling kit, what is the largest wheel/tire combo (staying with 17 or 18 inch) I could get WITHOUT modifying anything?

With stock wheels and your level kit, probably a LT295/70/17 to the LT305/70/17 size to avoid modifying, (some get away with a 34.5" LT315/70/17, and others don't), but there are no guarantees, especially if you go to a wider rim or even the same width with a smaller backspacing, like a 5" or 4.5". When they stick out more even a 33" 285/70/17 could rub. Unfortunately most aftermarket rims will stick out more, so your no modification rule will make your search tough.
[Stock for the 18x8 is 5.5" backspacing and for the 17x7.5" backspacing is 5 3/8"].

Here are the 33.5" to 34.0" models I could find that should work with stock rims and a level kit.
http://www.titantalk.com/forums/1012957-post19.html