I'm using the EVIC, hand calculating is impossible because of my mixed driving between work travel and pulling the fiver on weekends. The numbers are close enough for comparisons and line up with the MPG numbers other Cummins owners are seeing (cumminsforum.com, rv.net). I know most don't trust the MPG numbers vehicles calculate and display but I recorded for a year, the EVIC mileage and my hand calculated mileage on my 2013 RAM 1500 and the result, the EVIC read 0.8371 MPG higher than hand calculations. I don't know how to calculate the error factor in hand calculating but the EVIC averages over time. The experts all say MPGs start with your foot. I don't make jack-rabbit starts and I do not have a lot of start/stop traffic.
You are living in the past, the new emission equipped diesels (since 2013) are getting excellent mileage equaling pre-emission diesels. I haven't deleted nor am I going to delete any of the emissions, I'm happy with the performance I'm getting and have a 120,000 mile 8 year bumper to bumper Chrysler warranty that covers the emissions system. I smile when I wash the truck and see the inside of the exhaust pipe is cleaner than the outside of the exhaust pipe. There is a lot to rediscover about the 2013 plus Cummins/RAM solutions at
http://www.cumminsforum.com/forum/2013-general-discussion/