OK, just to clarify, at tickover at around 800rpm when warm the engine wobbles slightly on it's mounts more that one would expect and seems to be indicative of uneven running on one of the cylinders.
Now it could be down to a number of things but more often than not I find the engines run a lot smoother with problems lije this disappearing after having had the injectors serviced and valves checked. It could be something as simple as a dribbly injector or an incorrect valve gap that only shows as an issue at tickover and is less noticeable when driving normally.
Normally I wouldn't worry about it that much, it isn't that bad, however on the basis that Renate is planning a major trip in a couple of years time and with the mileage the truck has done I doubt that the injectors have ever been serviced and it's probably been a while since the valve gaps have been checked so I would be inclined to shedule that both are done prior to her trip.