Where did you check the Lift Pump Pressure?
If I remember right there is a Diaphragm Type Lift Pump on the Engine (I think they had a Push Rod that would sometimes break) and I know for sure there is another Lift Pump inside of the IP.
The Lift Pump in the IP is the one responsible for creating the Pressure that charges the Head and Pistons.

When it is Hot can you Here the Shutoff Solenoid clicking? If a Shutoff Solenoid is bad it starts showing up when it is hot.

When I ran the DB2s on the Test Stand ran the Pump and checked that it had the Max Fuel and got the Pump nice and hot and then dropped down to cranking Speed to simulate hot starting.
If it did not pass that it was normally wear between the Head and the Rotor.

The other things than can effect it are there is an Air Bleed Fitting inside of the Pump that is supposed to allow X amount of Fuel through the Valve and X rpms. Near all of the Pumps I worked had too much return Fuel.
Another issue depending on if the advance Piston is Steel or not is the Aluminum Housing around the advance Piston wears and while the Advance is not anything at starting Fuel is going around the Piston.
Also wear on the Metering Valve cause excess return fuel.

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84 300D, 82 Volvo 244Gl Diesel