Hey ghengis. You're not alone! And yeah, that little turbo diesel ram gets great mileage! I know some guys who have it.
I'm currently in North Dakota (only one more week and I get back to my Cruze!!!!) driving a 2011 Dodge Ram 1500 4x4 with a 5.7L V8 Hemi. It has a leveling kit on it so it sits up a bit. Necessary for the job.
I do a lot of highway driving up here and when I'm not fighting constant headwinds of 40 mph for 8 days straight, I can get tank averages in the 18 - 24 mpg range driving 60. I am lucky because it does drop down to 4 cylinders when cruising, even has a little "ECO" that comes on on the dash display lol.
I've been driving this truck for almost 4 months now and have had plenty of time to experiment. 60 seems to be the sweet spot on it. Either that or 45. 50 - 60 is okay, but cruising at 45 and 60 are the best spots for my truck.
You can check out my Fuelly log for my truck:
Christopher (Ram 1500) | Fuelly
The weather and wind up here do not help at all, but sticking to 60 has really helped. And I also run the highest octane I can get my hands on, which is sometimes only 89, but I usually try to put 91 in it. I have not seen any 93 up here near the Canadian border.
My advice would be up your tire pressure to what you're comfortable with (I keep mine around 50) and take your time to try out a tank where you don't go above 60 or 65.