On mine I have 63 gram weights, 36 degree helix, d&d pipe, y-pipe. Runs not 2 bad but needs a little more tuning. Call dons speed parts talk to Barry he really knows the M's. Also did you get the 09 ecu flash, made a big difference on mine.
I got one of the first 08 F-350 back in feb 2007, Got 80,000 km and the mileage and performance was best when i first got it. After they remap the ecu for the flame throwing issue the mileage and power dropped. Right now the way it is if I drive 110 km/hr I will get 13.9mpg to 16 mpg empty...