We went from a 550 to a 4400 series as well. We got the 9L but with a 10 speed. Has been a good truck with basically no year to year maintenance to date. The one thing that bugged me about the IH were the seatbelt pre-tensioners. For about the first 6 months every ripple in the pavement would make them lock and after about a mile you were pinned back in the seat by the belt. I had them change them out thinking they were defective, but the new ones were identical. I think the mechanism was finally beaten to death and now doesn't lock at all. The other irritant is the radio with it's tiny controls that you can't use while driving.