1999 Suburban or 2005 Yukon XL Denali

[Buckthetruck]

I am struggling with tow vehicle options right now. I have a 1999 Suburban with a 5.7l and a new transmission in it and a mostly rebuilt front suspension. It is geared with 3.42 (I think) in the rear so it is not real strong on longer hills. I pull a 1975 Airstream with it now and it does well with it, but it could be better. I am toying with the idea of a 1972 Suburban to tow it with, keeping what I have, or there is a local 2005 Yukon XL Denali with the 6.0 for sale for about $5,000.
My current one is fine, but it isn't great. The vintage tow would be cool, but safety concerns me a bit (my wife and 2 kids always come along when towing), and the Denali has me thinking. At that price, it has 240,000 miles but has a rebuilt transmission, new bearings, brakes, shocks, ball joints, tie rods, tires,... The guy at the shop ran down the list of things they have done to it (serviced it since new) and it is basically all new parts except for the motor itself.

My main questions are- how many miles does a well cared for 6.0 go for? Is it worth it to move up from the '99? (mostly considering the safety features and nicer finish) Or is the vintage tow just too cool to even consider anything else?