some of the SUV's got the 6 speed before it was ever offered in the silverado trucks.
Shawn I haven't towed with the Yukon's or Tahoe's of the era you speak of, but i have had a 2007 Silverado with 3.73 gears and a 4 speed, and I just picked up a 2009 Silverado with 3.42 gears and a 6 speed. Both 4 wheel drive crew cab z71's.
Sandwiched between those two trucks I had my F350 with a 7.3 and 4.10 gears.
I haven't towed back to back in the same day with any of them, or had a chance to weigh any of the loads I have towed. But I can say this.
My 2007 Silverado couldn't hold overdrive with a SUA YJ on 36's with a cage on a small lightweight car hauler. But it handled fine, you could feel the weight but it never felt squirrely even up to 80 mph+
My F350 would hold overdrive and 70 mph over the ziluakee bridge and felt solid as a rock with weight behind it, never even really felt the tires squirm.
Sunday I towed an E350 handicapped van with a big fiberglass top (wind sail) behind my new truck.
At 65 mph we felt pretty solid, over that it got a bit squirrely for my likings. I have to imagine this load was pretty close to recommended capacity with the van and heavy duty car hauler we were using. I held 4th or 5th gear most of the trip, but did drop to 3rd over the ziluakee bridge (but the truck held 65 mph at 3500 RPM just fine).
That said, I wouldn't be concerned about towing a jeep on a car hauler behind a tahoe/yukon. ESPESCIALLY if it has the 6 speed, its night and day compared to the 4 speed on the highway in my opinion.
What I would consider is air bags.