Father in law had a problem that was similar. More throttle would make it buck and snort at a higher RPM. He found a small crack in the top O ring on the fuel filter. Just big enough to suck a small amount of air, but it still started cold and ran, poorly that is. At this point on your tractor, I would crack all steel supply lines at the injectors/nozzles turn over engine and check for fuel. If the fuel has bubbles in it keep this up until it runs clear, no bubbles. If the bubbles persist, after a minute or more you are sucking air in from somewhere. If fuel clears up tighten fittings at I/N and start. Be advised: I am not a diesel mechanic, that's why I'm a TBN member!:thumbsup: Oh another thought, make sure you remove all old gaskets when replacing with new. 2 stacked o rings are not better than 1, and will suck air. Please don't ask how I know this!:ashamed: Let us know what you find, so we all benefit from this. Thanks and happy diagnosing. 445A