Help me decide how many days where

The Amalfi Coast and Naples are in the same area. You don't need 6 nights there. I would say 4 nights there at the most (if you plan to visit Pompeii and Capri) and give the other two nights to Rome. You cannot see enough of Rome with only 2 nights there.

Is this the order of your itinerary?
Where do you fly in/out of?

I agree with above that you need more time in Rome

Oh- okay- thanks for the edit/additional info.

Rome needs another night at least.

Assisi is a bit of an outlier and I hate to think of the travel from there to Amalfi Coast-where exactly are you staying?
Have you considered a stop in Orvieto instead? It's right on the train line and a much easier transit.

I struggled with same thing you are struggling with. So much to see and so little time. I would actually exchange Sorrento for naples. I found Naples to be crowded and not much to see. you can take an easy ferry to Capri from Sorrento and there are great hotels overlooking the water!

I just booked my northern italian trip and have 2 nights in Sienna which i am excited about.

Great problems to have!

Enjoy

Naples is a large, bustling city. Some folks prefer smaller towns and might like to stay in Sorrento or somewhere on the Amalfi Coast instead. But it is definitely not the case that there's not much to see in Naples, and Sorrento is a 20th century creation used primarily as a base for seeing other places; it doesn't have much in the way of sights itself.