Since we installed our cisco router interent is very slow

Recently we had created a VPN to 6 remote sites using the Cicso routers. Ever since we placed these remote sites on our network out internet is very slow and unable to send and recevie emails,it that slow. At times on the internet the page comes up fast, when you click on other pages from any site, it begins to hang. Our IT person cannot even figure this issue out, however prior to this VPN setup, all was working fine. We tested the interent speed and its ok, but not just over the network.