Insert randomly takes 10+ seconds to complete
Could be other sessions are causing blocking. See the Q&amp; A http://dba.stackexchange.com/questions/34313/identify-blocking-and-send-alert.

If the actual and estimated plans are the same, there's no point providing them, because they can't explain anything (aside from general inefficiencies that should apply to all executions, not just the slow instances). You'll could monitor sys.dm_exec_requests when it is running slowly to see who/what it's waiting on.

You can also monitor wait statistics (it could be severely bottlenecked I/O, for example). Reproducing in Plan Explorer might help here, as you can automatically get the wait statistics for your session (unless you fire up your own extended events session, you can only get system-wide waits on your own).

To capture what is going on during the potential blocking periods, you could also use Service Broker and Event Notifications.  Tony Rogerson back in 2007 posted a sample that reports on 10 second (or longer) blocks that you could use.

Also check auto-growth events and settings for the database and log. Occasional long delays can be caused by having to wait for a data or log file to grow.