Chris, I think the only time you need to call HTTP::release is if you've called HTTP::collect with no amount of bytes to collect specified. The only time I've needed to do this is to halt a connection until a sideband request is made to either DNS or an auth server.
Puli, as suggested above, HTTP::release shouldn't be necessary if you've specified the collection amount in HTTP::collect. Please do report back with what you find on resource utilization with the iRule. If you can also confirm the version of code and platform you're using it would help.
Aaron