I just finished installing my Stillen VK-Pro and added some Toyo Open Country A/T's (275/60/20) on my 20" American Racing Crush (black) Wheels. This is a great setup!! I really wanted the Pro comp Extreme MT tires but I got a screamin' deal on the toyo's and couldn't refuse.
The air kit and exhaust really needed the Stillen to get the best performance out of them. I think the extra hp really helps push those 20 " wheels.
Next up will be a lift/level kit!! What a truck!! I will try to get some pictures uploaded soon.
I would be curious to hear more feedback on the VK-Pro, especially from those of you running larger wheels.