Bought a low mileage 2005 Ford F250 XL Crew Cab with a 5.4L a little over a year ago. I needed it to pull a camper. Well, the truck acts like it is dragging when it's being driven and loses significant mph on even a slight incline when pulling the camper. The camper is way under the tow capacity (by almost 1/2) for the truck and I've had a mechanic buddy help me with going through the air intake and the exhaust and can't find anything.
Just this morning the check engine light came on and I have codes P0171 and P0430. I know it's not the catalytic converter because we just tested it a couple of weeks ago. At lunch today I'm going to listen to hear for a vacuum leak when I shut off the engine. I'm getting a Mass Air Flow sensor and will replace it Sunday, but does anyone have any other suggestions? I'd rather perform the work myself if I can...

 

You have to check for vacuum leaks with the engine running.

This is something you might consider having an experienced shop handle for you.

 

Will do. I'll have to get that done on Sunday and check back with the group. Thanks!