Same problem here - this has occurred after the 1.3 patch.
I have horrendous slowdown in the following situations:
- When fast travelling anywhere on the map
- When opening and closing the main menu
- When saving (including Quick saving)
- When loading
- When entering or exiting buildings (probably due to the auto-save)
Last night (Australia time) I was experienced freezes of up to 20 seconds. I have done the usual troubleshooting - hard resetting my console, deleting old save games and nothing changes this so the only conclusion I can come to is that this is caused by the patch. Considering the amount of time you spend entering and exiting buildings in this game, this slowdown makes it unplayable for me.
I hope Bethesda Support will update us on this issue and provide a resolution.
Hope we can expect a resolution shortly.