Gayan “Not Daddy” Perera is a man of few words when it comes to squeezing the last bit of performance out of on-premise installations. Succulent and straight to the point:
If you’re running CRM 2013 on-premise using IIS 8, make sure to go into the IIS Manager > Configuration Editor then select system.web\caching\outputCaching, set omitVaryStar to True and click Apply.
This will ensure that the CRM web resources are cached correctly. When this setting is set to False you’ll notice slow form loads.