autovacuum issue after upgrade to 9.0.1

We recently upgraded  from 8.3.something to 9.0.1.  With 9.0.1, we have a huge spike in vacuums every 8 days only on one of our DB servers.  We go from approx 20 vacuums every 5 minutes to 350 per 5 minutes.  This lasts for several hours, then stops.  I have attached a graph that shows the occurrence.  I am assuming that it needs to vacuum all of my tables to avoid some sort of wrap around counter.  I am wondering what is the best way to make autovacuum spread this out so it will not be quite a big of a hit.  I we did not see this with 8.3 and I kept the setting the same after the upgrade.