Ajax / Javascript & Other Debugging (Magento/NGINX)

Hi We have two Magento installs (test and production) - various bugs occuring with loading pages, load times and categories not showing any products. Also some Varnish settings are not perfect which might be adding to the problems. At the moment, we installed new Magento theme on a test site, and it uses ajax for catalog/categories, but it doesn’t display any products, even though they are there. Even our Live Magento site has been affecting - went from 2-3 second load time to 30-40s just since we installed theme. We think it’s a javascript issue, but would like to look at possible problems slowing down sites, and then fix AJAX javasripts bug causing Magento Categories to not display products and Magento Theme to not work at expected