since 3.4.1 I have noticed that logging in to my ACP is slow, and also once logged in, navigating back to the dashboard.

If only the main page is slow then a likely cause is the rss feeds used to pull blog entries and security updates from IPS servers. If I'm correct then all you can do is complain to IPS about it.

Though if you're having the issue then everyone else should as well... Also ensure that no hooks are conflicting.

The past week It is VERY slow logging in to my ACP.

For what it's worth, I've seen a few instances where an add-on that is making a callout to an external site (for version checking or what have you) by use of Dashboard Notifications can cause this. I can't remember the name of the add-on, though...