New here and my 2016 is new to me and my first diesel. I seem to be getting 21 mpg all the time in town and the highway. That seems low to me for highway diving on flat roads. I hope that I didn’t make a mistake buying this truck because I’ve heard the horror stories out there. I went diesel for the long haul. I buy vehicles and keep them for as long as possible. I love my truck so far and am researching deleting some things to help with longevity and possibly mpg. Or maybe tuning is the way to go. I don’t know. My truck is stock with 40k on it . Any advice?