Could be the slider images. The slider plugin you are using puts the slider images into CSS (as BG images) loaded at the top of the page, which means they all must be loaded before the page displays. This is not very good design for a plugin.
The better way to load slider images with with JavaScript that only loads the images at the end of the page load – meaning it will display as soon as the first slider is loaded. Weaver Show Sliders works that way.