ok, so... Found the problem. It looks like our system is struggling to cope with our 1+ million posts when it comes to the search index. This database table vb.searchcore seems to be getting out of whack every day or two then the site performance is abysmal. I optimize the table and we're back to normal. After some discussion with other board owners the best solution is to run a 3rd party search index application on the server and bypass this part of vBulletin. This removes the wonky vb.searchcore table from the equation where search then runs in it's own dedicated environment. Luckily there is a comprehensive plugin for this. All that is needed now is for the host to install the search app, I install the plugin and we should be good to go. Thanks