slow sites

Hi all,

  I have a 8GB vps from OVH running centos with webpanel. I have two domains with website on both domains. the sites are forums, smf and vbulletin. they run slow, sometimes the pages dont load so u have to hit refresh a few times.

this also did this on an older vps, the forums are slow to load, or dont load at all and u have to hit refresh.

so basically ive installed this all over twice and still the same slow sites. anyone know maybe settings somewhere?
thanks