It does sound like a Fuel Supply issue.
It still could be an air leak somewhere. I had a small Air Leak at my Plastic Primary Filter due to the Hoses being Hard. You could tighten the clamps but the Hoses had no elesticity to seal well.
Then if you have the Old style shiny Aluminum bodied Hand Primer that could leak.

Just to see and because it is easy to do; try swaping the Fuel Inlet and Fuel Outlet hoses (you need at least 1/2 tank to do that) and see if it inproves.

Check your Linkages to the IP and see if something might have slipped. Hold the IP Throtlle Lever while someone slowly steps on the Pedal and see how much play there is in the linkage before Throttle Lever trys to move.
After that have the Pedal Pressed all the way down and see if the Throttle Lever goes all the way to the screw stop.

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84 300D, 82 Volvo 244Gl Diesel