B8200HST power loss

[Rich7]

I have a B8200HST 720 hrs doesnt have as much power as it use to .trouble going up any grade in high range .Starts fine doesnt smoke has PTO pump and seperate fluid system for backhoe and engine bogs when using back hoe also So I think it is fuel rather than trasmission related just change fuel filter and cleaned air filter no difference . did run it out of fuel this winter and had a hard time getting it started again . The owners manual say insufficient output can be caused by carbon around orfice of nozzle piece ? do the mean injectors ?Any other ideas ?Thanks