Allis 6080 fuel issues

I have a 6080 we use to bale with, while using it this year it started idling higher and lower on its on and eventually dying. It wouldn’t start for a couple hours then once it did it would only run for a few minutes. Got it home and pulled the return fitting off and there was no junk or anything in it. Went ahead and ran a hose from the injector pump into a separate tank to rule out crud floating in the tank. It would just do the same thing. Hard to start and once it starts it’ll only run for about 5 minutes. The injector pump was rebuilt in 2020 at Cordell’s in Oklahoma. Any ideas would be welcomed

Thanks for the help. Blew the line out and the tractor seemed to start easier. It ran about 10 minutes before spitting and sputtering before dying again. That’s the longest it’s ran so far. I took the return line off and ran a clear hose into an empty bucket just in case that line was just plugging back off. It started right up again and did the same thing. Ran about 10 minutes and started sputtering erratically before dying.