Typically when ctrl-alt-del responds slowly it means your hard drive is thrashing.
Start by monitoring Chrome by keeping Task Manager open (set it to Always On Top from the menu). If you aren't familiar with Task Manager, you can start it by right-clicking an empty area of the taskbar or hitting ctrl-alt-del. With Task Manager running, try to reproduce whatever is causing the performance degradation. On the processes tab, you'll probably see the memory usage for a process start to skyrocket. That will identify the culprit.
Since Chrome runs a separate process per tab, there is either one offending web page doing this, or (I'd say more likely), a plugin is responsible.
If there's no rhyme nor reason to this slowdown, try disabling some plugins and browsing foe a couple of days. You might be able to narrow it down that way.