If you decide on diesel do as suggested take a long highway Saturday afternoon drive, perhaps take the wife out for a sat or Sunday brunch. When out driving put the exhaust brake on, will not hurt mileage and will warm the truck up faster. The 2013/14 3500 Ram diesels have a cold air/warm air door on the air intake, closes when cooler ambient temps and will remain closed till temps come up. (much like the old gassers where they took warm air off the exhaust manifold on cold start ups) The 2013/14 are your fathers Rams, they've made some great improvements over previous model years!