"So you are taking the train from Girona to Salamanca in the day?"

I thought the same, but OP does not mind.
3-4 hours on any train is my limit!

I'd consider taking a day from Granada (3 days was plenty for me and I'm a slow traveler and visited during a festival) and adding to Sevilla. You could hang in Sevilla for the day or do an additional daytrip (Cadiz, Sherry triangle cities, Arcos, Carmona, etc..)