We are considering a new tow vehicle.

I just replaced my old '98 Suburban 2500/454 and from what I've learned your Suburban with the 8.1 is a fantastic tow vehicle, too bad GM dropped it. I considered the Denali with the 6.2 but it's only available in a 1500, not the 3/4 ton. I wanted the 2500 with the bigger chassis, bigger brakes, etc. The shorter wheel base Tahoe with the 5.3 wasn't even a consideration for me. I can't speak about the Expedition except the specs on it aren't that impressive and it is also a half ton.
I ended up spending more than I planned and bought a 2013 GMC crew cab with the Duramax and Allison 6 speed transmission. This truck is awesome and I'm so glad I bought it.