Gordy, do you plan on analyzing your oil? I'm curious if the new tune is rich for safety, causing your lower mileage. A UOA might show high fuel dilution which would lower flashpoint and viscosity. Maybe the tech recommended 5W-40 because he knew a 5W-30 would be further weakened by fuel dilution.
Of course, this assumes the tech knew anything about your special tune
. Regardless, still curious.