I am speaking of vehicles that only use diesel fuel.

Personally, I am not sure what the diesel purges did to supposably fix the issues in the past.

Lots of diesel engines out there that never have any sort of purge done on the other than occasional additive in the fuel tank. When there is the slow down you are speaking of what I was taught is that it is most frequently a fuel supply issue.

Things that effect your fuel supply:
Plugged or plugging filter
Plugged or plugging fuel tank screen
If the fuel tank venting system is plugged
The fuel supply lift pump needs to be rebuilt
A problem with the fuel pressure relieve/overflow valve not holding the proper pressure (The spring inside gets weak over time, and some have plastic parts the warp or fall apart.
Crappy contaminated fuel

Unfortunately, there is no easy way to check the fuel supply pressure.

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84 300D, 82 Volvo 244Gl Diesel