A couple of thoughts here:

1. I went from 99 2500 Suburban with gas 454 to 07 5.9 Cummins Dodge 2500 Ram. Gas mileage with Burb: 9 mpg. With Dodge: 12 towing, 18 no tow.

2. Burb was a piece of crap. Never buy a Chevy again. Have heard the newer ones are better but GM lost me as a customer. By 150k I'd spent probably $6-8k replacing stuff that should not have failed, or failed that often (intake manifold, water pump, radiator, rear a/c, dash lights, brakes EVERY 15k, etc.).

3. Burb towed fine, not as good as the Dodge, but close.

Your mileage may vary.
[/b]
I think the new body style Suburban/ Yukon XL's have a much better build quality vs. the old ones. Also, the new brakes are truly impressive. I've got 81,000 miles on my 2000 Silverado 2500 6.0L and I've still got the original front pads. I had to replace the rears due to corrosion on the rear rotors that I didn't catch soon enough that chewed up the pads, but generally the factory pads last FOREVER. The only odd thing I've noticed is that when they get hot the pad material tends to deposit unevenly, which can lead to a braking vibration. I've only had it happen a few times and I tow a fair amount, just something to be aware of.

Someone earlier mentioned the K&N improving fuel mileage, I can can back up that statement. I was skeptical but when I got a FIPK for free I figured I'd give it a try. I normally get 11.5-12.5 mpg towing a heavy open trailer and with the bed loaded down, and I tend to run in the 75-80 mph range. Towed to KS in September and got 13.5 mpg for the first time ever, and I definitely wasn't driving any slower than normal.