I have a 04 6.0l f250 I use to tow a 7500# 5th wheel to a local ski resort. First trip up the hill this winter I noticed the truck loosing power pulling the longer steeper grades. Short steep or gradual grades and flat it is fine. Not towing I can't duplicate this issue. Pedal to the floor makes it worse. If I let off for a second it seems to help but it's short lived quickly dropping off. I replaced fuel filters and air filter. Helped a little. Took it to a local shop, had work done by them in the past and had good service. They did a contribution test. #5 cylinder was negative. Replaced that injector. Still lacking power. Don't want to keep throwing money. Any help or knowledge of similar issues, I thank you in advance.