My tunnel was working perfectly under 10.6 (10/10 on test-ipv6.com.) After installing 10.7, with the same setup I get 0/10 and this repeated message in the kernel log:
nd6_lookup: failed to lookup (the IPv6 address of my gif0 interface)
In spite of that, I'm able to ping6 the address of the remote endpoint. Thanks for any suggestions.
Have you tried removing and re-adding the tunnel?