What repair did you do that may have changed the governor setting? I don't have any information I'm not sharing, but if you did something that may have changed how the engine runs, I would go back and assess that first.
The other thing to try is to manually move the throttle lever where it enters the injector pump or governor and see if the linkage isn't delivering full movement. There may be a stuck pedal, bent piece of linkage, or something else that is keeping you from getting full throw on your throttle control.