why computed columns slowing down performance all the sudden?
I'm going to throw this out there, since no one else has mentioned it.

Having a scalar valued function in a computed column is an awful idea.


Forces ALL queries against the table to run serially (even if you don't select the computed column)
Forces maintenance (Index, CHECKDB) to run serially, even if you're
on Enterprise   
Executes row by row
If used in the WHERE clause, can cause issues with cardinality
estimates


Here are a few blog posts I've written about similar subjects. 

Still Serial After All These Years

Scalar Functions In Computed Columns

Scalar Functions In Check Constraints