So at around 50mph or climbing a hill, the truck will act like its puttering/ slight pulling and then let off and repeat until I accelerate and it stops. Ive pulled the codes and nothing is coming up? does this sound like a dirty fuel filter? Spark plug? 3rd gear on the transmission? Please help, wife and I are having a baby in a week and a half and want this taken care of before we got to rush to the hospital. thanks in advance.