SmartTrucker -
Welcome to EM! I'm looking for a NASA document that specifically tested truck aerodynamic modifications for fuel efficiency, but I can't find it. This is useful :
Reducing Aerodynamic Drag and Fuel Consumption
http://gcep.stanford.edu/pdfs/ChEHeX...0_11_trans.pdf
This is NASA, but not what I was trying to find :
Aerodynamic Design of Heavy Vehicles
https://e-reports-ext.llnl.gov/pdf/306864.pdf
CarloSW2