Tractor Repair: IH 1086 pulls down under load, throttle lever, fuel filters

Question
Arnie
I have a 1979 IH 1086, when under a load pulling any type of equipment or on road pulling up a hill,it tends to pull down (lose RPM's). If I bump the throttle up it picks back up. Is this a governor problem or something else?

Answer
  Change the fuel filters if they haven't been changed in awhile.  Make sure the throttle lever friction is holding the lever in place and the lever is not creeping back down.  If everything is OK, then the governor in the injection pump probably needs work.