Rails 3 to Rails 4 upgrade results in abnormally slow page load times

I'm upgrading an application from Rails 3 (latest) to Rails 4.0. This has resulted in page load times that are tremendously slow. In one case a page that previously rendered in less than one second now takes more than 4 HOURS to load.

We have been trying to profile the application and have gotten nowhere so far.

Before

Rails 3.2.19
Ruby 1.9.3-p547

After

Rails 4.0.13
Ruby 1.9.3-p547

[Also, I know this is not a great question as I'm not providing enough details. I will edit and add details as I get more info and/or if there are specifics you can provide me that would help me to provide additional feedback. I am not trying to be vague with my post. I just don't have shit to go on right now.]