I chopped both the muffler and the valve off and I personally think it sounds great. I drove from San Diego to Mississippi and back and it didn't bother me.
As far as DoD (aka AFM?), they make little modules that you plug into the OBD port to deactivate it, but I honestly recommend you get a Black Bear Performance tune. Probably the best thing you'll ever do for your truck.
I removed my muffler and the valve and just welded a piece of pipe in their place. It sounded great to me and V4 really wasn't that noticeable. Not to me at least. If push comes to shove, you can always just leave it and lock it in the open position with some with some wire or something. If you don't like it, you can always close it.
About the best I can do is show you my truck with a leveling kit on 33s. If you're going for style only, you'll be able to squeeze 35s under it but you won't get much use out of them. If you really want to go off road and get the most out of what you've got, the 33s will be better. 35s on a 4" lift will limit your articulation. Let me know if you want to see the Pic.
I installed an aftermarket Pioneer radio and slapped a camera under the transmission looking forward. My wife's not very good at spotting while offroad so this turned out really well. I can see where my tires are in relation to the trail. I can't remember which camera I bought but it wasnt very expensive.
I take it back, here's another link for the ones with the square main tube. It looks like you could set these up to be bolted on but welded is a lot stronger and can handle both the weight of the truck and repeated bashings a lot better.
http://www.chassisunlimited.com/product/armor-bumpers/chevy-gmc-armor/rock-slider-kit-sqaure.html
http://www.chassisunlimited.com/product/armor-bumpers/chevy-gmc-armor/rock-slider-kit.html
Check these out. They're the weld on kind (which are substantially better). Measure the length you want and order them. Only bad thing is the main bar is tubular and not squared as well as there's no kicker on the end. The kicker looks weird but it's SUPER helpful on tight bends. When I get back stateside, I'm either ordering some like these or I'm going to have them custom made. Before I got deployed, I had a buddy up in LA that was willing to make me some customs ones for the small fee of some beer and I buy the supplies. I kick myself for not doing it.
I've got E rated 285/70 17's w/steel wheels on my 2015 K1500 with a 5.3 and a soft tonneau cover. I also had BBP tune it for me. With AFM off and cruising from San Diego to MS at around 85mph, I was averaging 21mpgs. I probably could've gotten better if I set C/C lower but "I had a long way to go and a short time to get there."
Mine are either on the 3rd or 4th highest notches. I can't remember, It's been a couple of years since I did it and my truck's been in storage since shortly after.
My 2015 K1500 W/T. Nitto 285's and Bilstein shocks all around. I also had it tuned by Black Bear Performance. Looking to put a camper shell on the back when I get back stateside.