Are you using e1000 nic with esx 5.x? If so, thats probably your issue. Change your nic to vmxnet 3 or upgrade your host/vmware tools to 5.1 update 2.
After upgrading my host to 5.x, I ran into some odd issue. Some guest machines were dropping packets and having connection issues. Only the guest running e1000 nic had the issues. After changing to vmxnet 3, the issue went away. A couple of months later vmware released the following kb.