My GM literature shows that the Tahoe is rated for 8200 tow rating, with a weight distributing platform. But just 5000 lbs if you're towing dead weight on the ball. And the hitch on my '09 Denali shows that the hitch itself is only rated for 5,000 lbs dead weight.
So if you're planning on hauling a 6800 lb truck (Gotta love that Cummins engine, true work horse) you'll probably need a trailer that's going to be 1800-2000 lbs of weight too, for a total towed weight of well past the 8200 lb rating of the Tahoe. And that assumes you'd be using a weight distributing system. If dead weight, you'd be 70% over the capacity of your SUV. Would it do it? Perhaps. Is it safe or legal? Nope and nope