Why not go to the cradle of Sweden? It's a sort of Southern route to Dalsland, just a Little out of your way.
The original, medieval Sweden was cradled on both sides of Lake Vättern.
On the eastern side of Vättern there's e.g. Vadstena (home of the abbey of the only true Swedish saint, Birgitta), Alvastra (ruined abbey), Ekenäs castle (no historic significance but a real fairy-tale place), also Linköping (prettiest little old market town you can see).
On the western side of Lake Vättern there's e.g Åsle tå (typical row of rural cottages), Forshem's church (one of the most remarkable medieval churches), Husaby church and well (where the first Swedish king, Olof Skötkonung, was baptized in the year 1000), Skara town (where the first cathedral was built in Sweden) and of course Läckö, the magnificent, story-book castle on Lake Vanern.
You take the E4 south from Stockholm until Linköping, then go by smaller roads to the eastern shores of Lake Vättern, visit interesting places and then head north along Lake Vättern, round it and follow its western shore south a bit. Then you meander north-west across the plains of Västergötland until you hit the southern shores of Lake Vänern, go west until you come to Trollhättan/Vänersborg, right on the southern tip of Dalsland.
About three days should do fine.
Both Öland and Gotland are overrun with tourists in June (though it's even worse in July of course). Late May or late August are ideal times for visiting places so popular with tourists.
I hope to see you when you're in Göteborg, Judy!!
Welcome back to Sweden!