05 f250 crew sd 4x4 milage
 

I was getting 17 mpg in town and 21 on hwy with k&n filter and dna exhaust last fall now spring is here and its been cut in half. dealer is saying there is a tsb on a vacume line at the back of the head on drivers side. Has anyone heard of this???? also i run nothing but sythetic oil in everything including diff's..... oh its a 5.4 gas