I think your truck has the perfect look to it. 4'' and 37's to fill up that wheel well!Personally I think 37's look great with a 6" lift. I went with a Zone 4" lift and got 37's mounted up for a while. I lost about 1-2 mpg's by going from 35's and power was down but it wasn't too bad.
Here's a couple of pictures with the 37's.