take the filter housing off of the tractor. Then take the fuel filter out of the bowl. Look inside the passages up inside the housing for trash, specifically at the inlet side and also at the port that connects the inlet side to the filter bowl. If all clear, reassemble. Then perform a fuel flow test from the hose that comes from the tank. It should free flow with a very good stream and the stream should be about the size of the ID of the house (3/8"?). If it's slow, or dribbles, look for a restriction inside the fuel tank or at the tank outlet nipple.
If the filter housing is clear, the tank is clear then you have another issue. Perhaps a lift pump issue? Or maybe perhaps a mechanical engine problem which as long as it's never been hot and it's been maintained properly, would be rare.