My XC60 D5 Inscription (AWD Automatic) has been my daily driver for 3 years now and has been flawless untill recently. The D5 engine is the 220hp version, the car has done 105 000KM (65k Miles) without any problems and it even has 1 more year left of warranty.
It just went trough an oil and filter change at the dealer plus a software 2.0 update, which I did not ask for.

What followed shortly after the visit to the dealer was a problem where the car refused tho shift in 6th gear and after i shifted manualy, the whole car kept shaking and jumping rpm whenever I gave it gas.
I had previously experienced something similar with my 2010 XC90 D5 which had problems with the traction control system and some of the electronics. However, this time the dealer couldn't find any faults with the car and told me to keep driving it.

*Note that the following problem only occurs when driving on a highway with a constant speed, usualy 30-40 min into the trip and not always*

The first time this problem occured, I was overtaking on a highway in S- mode and the car reved up to 4000 something RPM (where it usually shifts in sport) in 5th gear when all of a sudden, the car fell on it's stomach and didn't want to shift up to 6th. What followed was me manually shifting to 6th and leaving the car in D where it started shaking every time i would give it gas. I can describe this shaking as if the car is trying to stall because the rpm get a little jumpy too. There were no faults on the dashboard (no check engine light, nothing..) and it felt like the car wasn't registering a problem.
I kept driving like this for the next 30km before I stopped and turned off the car for a couple of minutes. After it started again, the problem dissapeared and it drove normaly for the rest of the trip (about 120km).
A week later the shaking appeared again, between speeds of 120 and 160km/h *1000 to 3000rpm* (this time it was shifting well) but restarting the car did not fix the problem. As soon as I enter the city, problem disappears.

When taking it to the Volvo dealer, they drove it around and hooked it to diagnostics which showed no recent faults. Their response was just keep driving it, as if this is something normal.
As it is the last year of production on those XC60's, I thought such faults would have been removed by now.
I do not know what to do so I am asking if anyone else has experienced this problem or would have any suggestion on what the problem might be. Almost feels like faulty transmission or injectors, but the ECM should show a fault if this was the case.

At this point I am considering sellng the car or driving it untill something breaks.
Please advise and thank you in advance!.