Well, winter is here, so I'll make the recommendation that you indeed go with Bilstein shocks. I did, and I couldn't be happier. With a slight crank, add 4 washers to the stem of the front shocks before the bushings. Gives you another 1/2" of droop travel, which is needed with the crank. Much softer than the Gabriel Ultra shocks that I had been running, and yet more controlled than the stock shocks, especially in rebound. Even with a 1500lb camper in the back, the ride and handling are excellent. No regrets.
The 6.0L will work pretty hard in the mountains, but it'll get the job done. I recently picked up an '02 2500HD. Same driveline. It's working pretty good towing a 4000lb trailer, but if you keep adding throttle, it'll just downshift and keep ripping right along. 2nd gear at 60mph is about 4000rpm, and my truck seems like it could do that all day if I asked it to.
I'll have to check your website... I spent 5 or 6 of the best years of my life at Michigan Tech, and then 15 years in SW MI. I could move back to the UP, but I sure don't miss the rust. I bought an '86 Comanche out here and it just comes apart. I have heat to break off a bolt. My '06 GMC was bought from N. Dakota in 2009, and I moved to CO in 2010. It came with the paint already stone blasted from the rockers, and I swear it hasn't rusted at all. Soooo nice.