On the top of the injection pump is a fuel shutoff solenoid, I’ve seen the spring in these get weak and cause issues, you can remove the plunger and spring and reinstall the cap, it will operate and shut off fine without the plunger, easy and worth a shot, also check the temp sensor on the pump, big threaded connector with two wires, have see the terminals burnt many times in this , Deere used to offer a repair pigtail but I haven’t worked on one for several years so not sure if it’s still available .