The Yukon 2500 is also on a 2500 frame with 3/4 ton axles. You're comparing apples and oranges.
The OP is looking to push the tow limits of his truck past what it was designed for. Thinking a simple re-gear will get him to the tow limits of a pickup truck. There is a whole lot more that goes into determining towing capacity than gearing ratio.
What he said times a million.
Even if it's true that the newer trucks with the "Max Towing" package came with a larger rear end, I'm having serious difficulty with the theory that swapping your rear axle assembly is any cheaper and/or easier than doing a simple gear swap, especially if you'd need to source one from a modern (two or three year old) truck. Even if all other things were "equal", which they most decidedly are not.
And don't forget the point I raised earlier - if you own a 4WD/AWD truck you're still going to have to re-gear the front to match, whether you do a simple gear swap out back or replace the whole axle assembly.
And you still won't have a bonafide (and safe) tow package. Axle ratios, axle size, frame, brakes, sway bars, springs, shocks, cooling, proper hitch, etc. There's way more to it. Not to keep beating the poor guy up, but the OP is trying to take a short cut, and that's dangerous.