Thanks, I believe that was the problem. I pulled the assembly, not sure what its called, and the filter had some junk on the screen. Cleaned it all up, and the tractor seems to be back to normal.There is a plastic filter screen in the back end of the injection pump where the fuel line comes in. Item #30 in this breakdown. Check and make sure that it is clean. A lot of people don't realize that it's there.
I do know that "cover" assembly (#39 in the schematic) houses a bunch of different things, including the filter...several springs, some sort of hydraulic valve, and a couple of other random parts. The schematic doesn't really show how everything is assembled, at least not very well. Reassembly had me a little nervous...