The Icon truck is running a 315/70/17 which is a 34.5" tire. They also run a 17" inch wheel so it does clear the caliper. The Icon wheel is 8.5" wide with a 4.75" backspace and 0 offset. According to Icon you can run a stock wheel, but they do not specify what 18" tire size.
Why do people keep referencing the test done on a GMT900 5.3 from BlackBear? While the engine displacement is the same the engines are very different. As an owner of a 2011 I would use an Air Raid intake tube, but someone has not done this testing on the newer 5.3.