2011 6.0 to 6.6 Duramax

[Sierra6.0]

So our needs have changed. Even though we've loved it, our 2011 2500HD CC std bed Sierra has only 20,000 miles on it (still smells new), but we need more payload. Right now we are considering a slide in camper with enough tow capacity left over to tow our Land Rover Discovery 2 (4500lbs) to various off-roading and camping sites around Utah.

 

This puts me in Dually territory. Ideally, 13,000+ GVWR, which means I can only consider 2011 and above.

 

That said, recently a used Duramax Dually has popped up in my area that would essentially be a wash in a trade (actually my monthly payment would drop). My biggest concern is mileage. The DRW has 101k on the clock (appears to be highway, no off road body damage, rust, etc), and my Sierra is spanking new at 20k. Looking at KBB, the prices are actually a wash between my car/condition and a dually diesel @ 101k miles, so I don't think it's a bad price.

 

I'm an avid DIYer and quite familiar with gassers but have never owned an oil burner. Is this even a good deal? What kind of costs in maintenance am I going to see with the Duramax/Alison at that kind of mileage? What kind of high mileage overhauls am I going to need to start saving up for?

 

Opinions welcome.

Thanks!