I've got a set of 39.5 x 13.5 - 17 IROK's for mine....great tire. Your coarse spline rear pinion will be a major weak point, but it is regardless. Longs/chromos will hold in front, but your knuckles will be the next to go.
I ran a set of 37 x 13.5 - 17 Pitbull Rockers this past weekend....IMO, they performed as well or better than the IROK's on everything, and were amazing on hardpack steep climbs...I've never had a tire with that kind of traction on launches. Tried a climb in 1st with zero approach, and they tossed major ground as they bit in...tried the same climb with a 2nd gear launch, and it zipped me to the top so fast I wasn't sure I could stop...two of the guys with me are truck pullers and they claimed to be ordering a set immediately just on the tire's performance on that one climb.
The clearance advantage of the 39.5's was the only issue, but the truck still made quite a few lines that it has failed at in the past.
I'm VERY torn now between keeping the 37's as my only tire, or keeping both sets....I was positive I'd like the IROK's better, but am not so sure anymore.... (see the Attica pics in TrailRides)