Have you got enough JK listeners/connectors for your load? Do you notice any content serving issues when this problem occurs? Are there a batch of requests that happen when the error occurs? Have you tried changing the connectionTimeout value to see the effect? And is there anything different between the two set ups - e.g. different OS? You could also try changing the enableLookups false to cut the DNS search delay, but this is more of a longshot.
I'm not sure if there is much more to offer. You may want to check the Tomcat e-mail lists if you are still stuck and can't deduce anything more from these suggestions.