I agree with Dave. Some more things that could be tested:
- Did everything became slow, or a few sessions? If everything became slow, than we have to suspect the setup, else we have to determine what has changed.
- Do you have a dedicated network between app and db server? It is advised to do so as the application server can generate quite some traffic.
- Can you check if the connection is setup properly? Can the the database server be resolved quickly etc.
Hope this helps,
BTW: this post has been made on my personal view. My employer might not share my point of view.