Can I ask your average MPG with your 8.1? I'm looking at one myself and trying to figure out the "real" costs to run it vs. a 6.0 or my current 7.4. I like the 8.1 torque and don't have the budget for a diesel. Mostly farm trailer tows and a bit of running kids around town.
If you don't mind I'll chime in on gas mileage for the 6.0. I have a 2014 GMC Sierra 2500 HD with the 6.0. It has 37,000 miles on it. Around town it never gets as much as 11.0 MPG.......more like 10.6 - 10.8. On the hiway it does much better. I make frequent runs to SeaTac from Lake Stevens, and it gets 16.3 - 16.5 at 65-70 MPH. I just drove over the North Cascades yesterday and it got 14.2, carrying a decent-sized load of hunting stuff.......ice chests, etc.
Pulling my 25' (5800 lbs empty) camping trailer it ain't good. The best it gets is 8.6, and sometimes not that good.
Hope this info helps.