Dubshot, welcome to the forum!
I have an '86 custom van with a plain 6.9, no turbo, no modifications, still with "the soup bowl" like some here like to call the air filter canister. The whole van with the tools inside and some more stuff that I carry just in case, weights about 9,000 pounds. I pull with that van my trailer with my Massey 431 and two implements (the harrow discs at the front of the trailer and the tractor with the mower). The trailer plus the tractor and implements weight is about 10,000 pounds. My van has a C6 that hauls the whole group nicely, we have some hills around here (although not as steep as yours maybe) and it goes fine. I don't like to run more than 55 MPH when I'm towing the trailer because it takes some time to stop it on dirt roads.
The other day when I was getting home after a day working at a friend's property, it was about 8 PM and a deer that was walking on the road jumped in front of me into my property, right when I was pulling into my drive way. I had just enough time to stop (the trailer still halfway in the road), jump with my 586 in hand and put a 158 grain .357 magnum in the deer at about 50 yards. It run for some time until it drop at the back of my property. It was a good day working, that gave me some cash and some meat to put on the table. I thanked the Lord for the strength it gave me to work, for my old truck, my trusted 586 and the eyesight that still is good enough to enjoy our favorite sport down here where I live: plinking!
Burt.