How well does it tow something like a camper in the mountains? - You wont know a 7500lb camper is even there.
Do the Rancho shocks make a difference in towing? For example does it squat lower with a load? You won't squat significantly with this camper.
Is there a need for the Heavy Duty Front Spring / Camper package and can it be added on later? It is not that much ($45), but I am having trouble finding one with it installed. - I have the camper package and tow a fifth wheel. I wouldn't get it again as it rides rougher when not towing.
How well does it ride for an everyday driver? - Like an empty dump truck. It's happier when towing.
Is it taller than the other Sierra 2500s? I read that it has a 2" lift. - No idea.
Would it be better to spend the extra $1k and get the 3500? I have heard that the ride is very similar. - If you need the extra payload capacity.
What kind of fuel economy are you getting? - gas engine. 8mpg towing, 14mpg everywhere else.
In your opinion are all of the extra features worth it? Of course I want it to have everything, and having blank buttons drives me crazy, but am I going to spend a butt load and it not be worth it when I could just get a SLT with just a few features, or get an AT4 without any extra packages? - Not in my opinion. I have the Custom and am perfectly happy.
If you got the AT4 do you wish you would have got a Denali or saved money and got a SLT? N/A
What is your favorite feature of the truck. - It tows my fifth wheel.
Does the SLT come with the multipro tailgate? All of them that I have found online do not have it, but the brochure says that it is standard on the SLT, AT4, and Denali - No idea.
Sounds to me like you're going to spend a lot more money than you need to. A 1500 would be a smoother ride and tow a 7500lb travel trailer a few times/year just fine. If you want the truck go for it, but don't convince yourself you NEED it to tow this specific camper.