Usually the dealer will test the fuel to determine if it's bad and then blame the part failure on the fuel supplier. Sometimes it just happens though and parts fail.
I haven't done any "emissions updates" so my MPG is still decent. My driving style/route has changed a little bit as I'm doing more city driving during the week as I moved closer to work.. I'm averaging around 34 though even with the city driving. I've still hit 40+ on all highway trips.
It's likely the tune is conservative due to EPA guidelines on Nox output, etc... we all know, the more power, the more technology that's required to clean up and make it meet emission standards. Ram probably felt like they found that "Happy Medium" area.
You can get the official manual here:
http://www.ramtrucks.com/en/owners/manuals/
Then choose the diesel supplement option. You'll see they have a chart.
From manual:
So, basically it could go up to 10K miles, and as little as 3500 miles.
Welcome to the site!
That was my first impression. But, if they are draining non-sold trucks oil and replacing it with the new spec that really takes away from the "cost saving" theory.