I would actually spend the 2 nights (is it nights or days?) in Trier. I had a very long list of things to do there and did not get them all done, mostly because my tour was at the end of August and there was a heat wave in Trier! The Landesmuseum is excellent altho much of the signage is in German I could figure much of it out. There also are the baths, Porta Nigra, 3 big churches, Marx' home to name a few.
https://www.trier-info.de/english/sights-in-trier
Although there is a walking tour of Trier the first morning of your tour there is not really enough time to go in to anything (altho our tour did do a quick stop of the Roman baths). It is also generally a Sunday morning so the churches are having services and not really open for visitors. I'd recommend you do the churches the day before if they are of interest to you. Another tour member and I were in the Dom and happened on an organ concert on that Saturday. We paid the 2€ (!!) and listened to a terrific recital. Very fun.
Right after the walking tour you will get on the bus and head for lunch at a restaurant on the Mosel and then continue to Burg Eltz castle. By the time you get back any sights will be closed so no time on that end of the day either.
Several of the people on my tour also took a day cruise on the Mosel which they enjoyed.
The tour departs for Baden-Baden after Trier.
This is a fun tour!