I had a similar situation when I started Latuda. This is a new mood stabiliser which has worked very well for me. Unfortunately I came down off of Effexor far too soon and had one of the worst depressions in recent history. It's taken 8 weeks to get out of it which included restoring the Effexor to about 60% of the original dose.
Whatever change you do make I strongly suggest you make it EXTREMELY slowly! I just couldn't wait to get off Effexor and it's side effects and was somewhat devastated to discover I still need it in my cocktail.