The backhoe in the morning starts runs good for about 20 minutes then it like runs out of gas but does not quit it stays on low idle with no power for maybe 10 seconds then speeds back up for another 10 seconds
Huh? the slowing down is typical of the outlet fitting plugging, typically from the governor ring disintigrating. But the speeding back up is typical of sucking air? Try taking the fuel cap off when it does this, then check for fuel line cracks in the rubber suction line from the tank to the fuel transfer pump. Last resort, take the return fitting all the way off the injection pump and blow it out with a garden hose and air compressor, it should be a check valve and may only flow one way, but you can still clean it both ways with a pin.
There is a vent in the fuel cap if it is clogged it will cause this problem it’s on bottom side of cap there is a drilled passageway in center of cap to the mesh vent can be cleaned with parts cleaner and air. Also there is a fine mesh screen on the fuel pick up tube inside the fuel tank over time it can become clogged with fuel allege. I don’t remember if you can remove the tube on the D without lowering fuel tank but you do on the E series because it is part of the fuel sender. Hope this helps I worked on Deere construction equipment for 38 years my recall is a little slow but I still can remember all the problems I encountered (eventually).
I used to keep an extra cap on my service truck cause some of those old caps had like a brass mesh pressed in there..