The REAL question is: "What does the Gulfstream AND the trailer AND all of the stuff IN the Gulfstream weigh?" That figure is your gross towed weight.
My 232 has single 300 HPDI power, a 15 hp kicker on an Offshore bracket, a radar arch, and a bunch of custom cabin shelving (Starboard) that I installed. My gross weight is 6200 - 6500 lbs, depending on what I carry in the boat (downriggers / weights, tackle, ice, food, clothing, etc.).
There are probably guys on this board - 232 owners - who will tell you that their Gulfstream tows at close to 8,000 pounds (fuel on board, water on board, twins, gear, hardtop, etc.).
I too view my Avalanche as a vehicle that must be fully capable of pulling my boat, but THAT is not the truck's primary function. That is why I ordered the 3.73 axle, which gives me 19.8+ mpg on the highway - nontowing.
Your truck will handle the boat. I would NOT tow in OD range.