So I know you are trying to "fix" new posts.
As of a couple of days ago, when I click New Posts, I get posts from the last 4 days, regardless if they are new or not. Just the last 4 days worth. Okay, I can live with that, because I know when my last visit was.
However, now if I click New Posts, then wait 20 seconds and click it again, I get completely different results! Huh....go figure.
You might want to consider removing that last change. It's clearly not working as you thought. This is the first forum that I've seen that has issues with the New Posts functionality in vBulletin. You might consider opening a call with their support.