How to shorten the wait period between clicking on thread and page changing?

[asabet]

On my sites, when I click on a new thread title, there is a pause of up to a few seconds before anything happens.

Here is one of my sites: http://www.mu-43.com/

Now here is another vBulletin site (not mine) where you click on a thread and the page changes immediately: http://www.diecastmodelaircraft.com/

I understand that my pages takes a while to load because most of them are full of large photos, but I'm talking about the pause that happens before even getting to a page.

What is happening during that time after clicking on a thread title before the page switches, and how can I speed it up?