This is more of a general question. Is it possible for a huge upgrade (such as from 1.4 to 1.9) to cause a site to slowdown especially on the backend?

Sorry if this is the wrong section for general questions.

To be honest, I am not 100% certain, but I doubt it. I've had this problem before (versions 1.8 & 1.9) but it was related to the hosting/server issues. Has your hosting changed in any way since?

Thanks for the reply, fearmydesign.

To answer your question, we moved the site to a dedicated server after the upgrade (and when we noticed the slowness after upgrading). What my system administrator noticed was that the PHP is pulling up all the processes on the server.

He suggested we implement a caching module to fix the issue since he believes it is not a server issue.