Contact Hostgator for help if you are sure it wasn't your own connection making the web site load slowly(if it continues). Six domains on one hosting account is nothing. You shouldn't be experiencing any slowness because of that.

Could be something on your end or something configured wrong using more resources... .02.

Maybe it's just the content on your page..?

It could be a high res photo, backgrounds, fonts, video, music?

Are all your hosted sites slow or just this one?

Optimize your HTML code, Make sure that your site doesn't have any unwanted tags or broken links and that it is optimized for load time. Errors on your web pages can slow down your website - Make sure your website is error free!

Just contact Hostgator about this , or try to optimize site , may be there was errors in your wp site ,
I am currently running 40 sites on my single shared hosting and all are running well . So thats not a issue .

The extra use of Javascript and flash on the site can also be the reason of making the site slow.
When a user opens the website all the data of site text, image, each and everything first downloads in the user system and then this data displays on the browser so if their is heavy and many data on the site it will take bit long to download all the data on user's system which increases the load time of the site