An add a leaf would be the better option of the two. The tires I currently have really set off the whole stance IMO. Check the 04-08 section later, I'm about to try and add some new pictures from this summer.
To be honest couldnt tell you. Since I have the fx4 package, im assuming my rear sat a little high than yours did even when it was stock. The 2.5 should level it out like it did min, but it still may not sit as high.