I have a very similar problem.
I am running many sites all using the Ultimatum theme, as of last night when the 3.8.3 auto update happened my admin panels are all painfully slow.
I have many sites on different servers and they are all the same. When I switch the theme the problem goes away, so I know it was caused by the auto update and has something to do with the ultimatum framework I use.
My first thought was to go to Ultimatum Support and see what I could find, and to my surprise and great depression, the site is GONE. All references to it bring back page not found. UGGG
Since I have many sites I have developed using this framework I am hoping there is some sort of fix on the server side or the wordpress side.
Any thoughts?