29 Combined mpg!

I had a 98 Ram 3.6 six banger gas. It could barely make it up grades at 65 mph. It got 16mpg and was loud, the steering loose at 200k and I finally had enough. I bought the 2015 3.0 liter diesel Ram 1500. The high torque keeps the speed up on hills. The mpg gauge after 500 miles is reading 29mpg average combined! Before I drove around the city, the highway mpg was 32. My range is over 700 miles on a tank. Yes, my accelerator foot is light as a feather and I don't go over 63mph usually. I have floored it once after being warmed to help break it in. I will do that once every couple hundred miles. I used Power Service fuel additive which increases the Cetane rating. I found DEF at Walmart for half the cost. I am wondering if there is any other way to be thrifty on that stuff. I have heard parts are hard to get so I am already buying my Rotella synthetic T6 5-40 although Ram says to use 5-30 but in Texas summers, I want the higher number. Buying the oil 3 gallons at a time saves bucks too. I got the oil filter for 16 bucks instead of the Mopar at over $40. I use GasBuddy.com to find the lowest diesel price., $1.45 in north Arlington, 20 cents cheaper than the south side of town. I keep my tires at 44 lbs, maxed. I bought a Spectre air filter because it is supposedly as good as the K&N and just 30 bucks through Amazon.com but have not received it yet. I have thought about drilling holes in the plastic housing. I saw some "smart guys" on another forum blast some guy for doing that, but why does an open one have better flow than a closed on? DUH!!! I ordered a Smitty tri fold tonneau cover. FYI, 6061 aluminum is much stronger than 6063 which Tonno uses. This should help highway mpg as well.

I noticed something about a tuner. I have no idea what that does. Can someone help me with some information? Any other ideas for this great vehicle? My last new vehicle was a 2007 BMW X3. This truck is much better! If you are thinking about buying this truck, I strongly recommend it!