let's see - assuming you bought your '09 in 2009, and this is now 2019. Given my limited math skills, that's ten years during which you drove 800,000 miles.
Wow - you average 80,000 miles per year? That's almost 7,000 mi. per month. What are you telling us - you do OTR with a Durmax ?
Assuming what you have posted is correct, can you tell us your secret to keeping your vehicles serviceable ? Oil change intervals. Oil & oil filter brand? How often do you change automatic transmission and gear oil?
I work in the telecom sector, cover all of Oklahoma and into Ks, Ar, & Mo.
If I leave the house, it's usually a 250mi round trip. 400mi day's aren't uncommon.
The only thing I did to the '09 was brakes and front spindle sets at 300K mi. Oil changes within a coupla thousand miles of when it told me to.
The '11 had been tuned and deleted. Ran it with the 100hp bump.
It got a tranny controller, 2 water pumps, brakes & front spindle sets at 365K mi. Had to add some differential juice about then. Changed the Allison spin on filter at 200K, or thereabouts.
I had run Lucas fuel treatment, then caught a whim to use the Power Service. I think the cleaning action of the PS may have caused some issues.
I run Rotella and Fram XG9100 filters.
The '16 High Country had 42k when I bought it a little over a year ago. It has had head gaskets (warranty) and the DEF system is dealing me misery. Just rolled 115Kmi.