OhioRVHawk, lots of people have put in their opinions and they are all good. When I knew I was going to get a 5th wheel (Monty 3400) I debated between a 3/4 ton and a one ton. I have NEVER regretted getting the 2008 one ton GMC K3500 (K stands for four wheel drive) and it was only about $1000.00 more. Money well spent. Since it was going to be my "retirement rig" I went for everything. The SLT package, which included pretty much everything. Heated leather seats (BOY do I love those), power sun roof, extra cab (NOT crew cab) 8 foot box (only thing you can get with the one ton) and all the other goodies. Personal choice, I went with SINGLE rear wheels instead of dual ones. Reason, this rig is also driven and parked "in town" so the duals just stuck out too far for me. I have had NO problems with stability towing the 3400. The Duramax/Allison combo is great. It just "walks" up the hills with no problem. The downhill "grade braking feature" works very well too.....once you get over hearing/watching the RPM's hit 33 to 3400 RPM, but GM reassures me this is quite safe and normal. As far as mileage, I set my cruise more for RPM's then MPH. On the open road, I set it to maintain about 16-1700 RPM, which is about 60 MPH. The Duramax's peak torque range is at 1600 RPM, hence my choice. It very seldom shifts down, and I get 11 to 12 MPG. As they say, it is an individual choice, it's whatever you like. We are just saying what worked for us! Good luck.
I just looked again and noticed some talk about traction in snow. Last December, Portland (OR) had the worst snowfall in years. Some places drifted three feet. I know, I know, some MOC'ers will laugh at that, but Portland is famous for RAIN, not SNOW. If we get an inch, it shuts the city down. Anyway, I had to get to work, so I filled three drums of water in the back of the truck. NOTHING stopped me. Traction was great, and never slipped once. When done, just tip the drums over and drain them out. Anyway, just two more cents worth. Hope it helps.