I apologize if this is old info (it is old, based on the cost of diesel quoted in the paper), but I haven't seen this before, and others may not have either. It's obviously directed at big rigs, but there is a lot of useful information for us.
http://www.cummins.com/na/pdf/en/products/truck/MPG_Secrets_Whitepape.pdf
http://www.cummins.com/na/pdf/en/products/truck/MPG_Secrets_Whitepape.pdf