Hello ronswanson1
Thank you for your question.
In general, a class upgrade ticket is the ticket you need if you already have a second class ticket but wish to travel in first class: you pay the difference in price and purchase a class upgrade.
Do you already have a second class ticket or a GA travelcard form Interlaken to Bern? If yes, then it is correct: you may travel in first class thanks to your class upgrade ticket.
A GA Travelcard is an abonement allowing you to travel in the whole of Switzerland withour buying a ticket every time. If you have this, it is correct to pay only for the journey from Basel to Strasbourg (abroad section of the journey).
Make sure you have a GA Travelcard: 1-month GA Travelcard | SBB this way, you can travel everywhere in Switzwerland without a ticket (you will only need a class upgrade if you wish to travel 1st class)
Please call our colleagues at the SBB Contact Center (0848 44 66 88, CHF 0.08/min) to verify the details: seeing the tickets and/or travelcards you have, they will be able to better answer your questions.
I wish you a nice day!
Regards,
EleonoraS