A few things...
Wheels/tires
1)Wheels in the first pic are of GM factory 20's. Same as I have on my truck.
2) wheels don't affect speedo reading, tire diameter does
3) GM factory tires are ~32.8" diameter
4) you con go with a beefier wider and only slightly taller tire without affecting speedo. Mileage will take a hit though. I run 305/55/20 and my speedo is only off by 1MPH.
5) taller rims (assuming same diameter tire) will ride a bit rougher.
Leveling
1) in stock form these trucks have ~3" rake.
2) Leveling kits generally do just that and raise the front 2.5-3". When you tow you'll be nose high unless you add air bags.
3) you can take some of the rake out of these trucks without affecting ride quality. This is done by cranking the torsion bars but you have to be careful not to go to far. I did 6 turns in mine which raises the front 1.25". Put on a set of Bilstein 5100s and it rides really nice.
BTW beautiful truck. If you haven't already found the duramaxforum.com I recommend you check out their tire/wheel section to get some ideas.
