Latency between an IIS server(2003) and an F5 vip, any ideas ?

I have an asp .Net app which calls an F5 vip internally. Now when I try the URL of my .net app, the homepage takes around 60 seconds to load, however when I replace the F5 vip with a direct back end server URL, the page load in less than 5 seconds. when I try the F5 vip or the back end server direct URL, both load pretty quick through my browser. The latency is only seen when my .Net app(IIS6 - win 2003 server) calls the F5 vip. Has anyone faced or heard about such issue before ? Any help will be greatly appreciated.