On this engine
with high mileage its common for the injectorsd to need recalibrating .
I would first cneck for any malfunction codes . fuel pressure could be your main factor for the problem you have just as you are thinking .
Start with a basic tune up, change fuel filters check fuel for water content .
Use a good fuel injector cleaner for diesel injectors .
Take a few days drive see if improves..
If not see if you can get the engine on a scan tool and check the system completely by putting the engine though a few test for the fuel system in live data a good Volvo diesel tech will see what is good or bad data .
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Kind regards Greg