Any experience here with driving SS38, the Passo dello Stelvio? Particularly in later September?
It is a very, very slow climb, extremely twisty on the Merano side, and very popular with cyclists, so actually not that pleasant to drive.
But the views are incredible, and the road is fairly wide (2 normal cars pass each other with some care but without manoeuvering) so it is not particularly scary in my opinion - for the driver, at least.
The descent on the Bormio side is much easier.
It is an "iconic" road, so if the weather cooperates, go for it!
But if the weather is less ideal (cloudy, wet), or if you would rather have a smoother drive, then my suggestion is to go via St Moritz. The road is excellent and the scenery is stunning as well.
Late September might bring rain, but usually no snow - in any case, don't attempt the Stelvio in rainy weather.