Stay far away from the 360, my 01 ram van with the magnum gets 12.3 no matter how I drive it. On a good day sitting in driveway without it running I can get 17-18 mpg
You must have purchased the "lean sip" version. My 2002 Van with 5.9 is 11mpg. Foot in it, foot out, around town, on the hwy, stock clapped out engine, new rebuild with goodies, rolling down the backside of a mountain...