The SCD transformation can perform badly when compared against other approaches.
What type of SCD are you using?
When I refer to a set-based approach, I am referring to performing actions on groups ('sets') of rows concurrently, rather than using any sort of looping. This is usually the standard and optimal way of working against data which is held in a SQL Server database.
If you haven't even tried to resolve your issue, please don't expect the hard-working volunteers here to waste their time providing links to answers which you could easily have found yourself.