Unknown Problem

[truck26]

I have a 2006 F350 6.0 that seems to possibly have a fuel problem. The truck seems to idle low and than high and just runs pretty unstable. Occasionally the truck wont start after I shut it off, then will take up to a half hour to restart. I have taken it back to two seperate dealerships in NJ and both have said there is nothing wrong. The fuel mileage dropped from 17.9 MPG to 14.1 MPG. I love this truck and would trade it for the world but its just starting to concern me. The only mods that have been done to the truck are a 4 inch silverline cat back exhaust and 2.5 inch level kit. I used to have a SCT SF3 programmer in but took it out in fear that Ford would blame the programmer for what ever might be wrong. I would appreciate any help. Thank You

[jamstoyz]

maybe put the sct back on to see if it throws any dtc's than go from there.

[symbols]

[jhaddox]

if its happend recently its because of the winter fuel blend they use, it has more anti gelling additives in it so your milage will suffer during the winter

and the idleing goes up and down when its sitting just idleing it park its the high-idle feature kicking in.

the starting i have no idea...hopefully a tech could shine some info on it