Hi Tom,
We're working on finding a better way to implement the slider like QLab 2 had, but while it was handy in some cases, it didn't really work as well as it should have, so we're rebuilding this sort of function from the ground up. That's just going to take a bit of work, so I can't promise exactly when it'll happen.
In the meantime, have you tried the Load to Time function? Just hit Command+T or choose "Load to time..." from the Tools menu, and you can manually enter a time to load to. This is actually a lot more accurate than the old slider was, although obviously it can't scrub, you have to know where you want to load to. It doesn't solve all the cases where the slider was useful, but for a lot, it's just as good, if not better!
-Andy