I have WP Super Cache enabled and configured according to HostGator's recommended specifications (we're hosting on HostGator). We have a reseller account, so the CPU usage is not actually accessible through the cpanel, but yes, we're on a shared hosting plan.
When it loaded within 3 seconds on pingdom, it was when the NextGen Gallery was deactivated, so when I enable it, which is what is the case right now, it loads a lot slower. According to HostGator, NextGen Gallery is what seems to be causing the CPU overage, because when they send the report of why it's getting temporarily blocked, all the pages that are experiencing the issues during the time of the report being generated are using NextGen Gallery and the URLs point to them galleries int he links they provide as well.
Do you happen to know if we upgrade to the premium version if this would help? Could it be some issue with having too many galleries and using the free version? We do have quite a bit of galleries, as it's a modeling agency website.