I have a 1995 F350 w/ a 460. Four wheel drive. The truck really struggles to make it up hills driving on regular pavement. It doesn't jerk or anything, I just really have to gun it to keep going and it is still slowing down. RPM's are not. I replaced fuel filter. Could this be my injectors ? What about a bad fan clutch causing power loss ? Fan belt too tight ? I appreciate any insight to this problem. I can barely carry any load in the bed, and it certainly wouldn't pull a trailer !