IS-IS and IPv6 in equal cost path topology

Network of 7609s running 12.2(18)SXE3. Two
equal cost path links between each 7609. IS-IS Level 2 routers only. When pinging an off campus IPv6 host every other packet is lost. It seems like the equal cost paths prevent an alternative path off campus but that path isn't working.
We cannot figure out where to look next.
Any thoughts ? Is this possibly an IS-IS
issue ?
Thanks

OK. I'll try. We have 5-7609s running 12.2(18)SXE3.
Each 7609 has a variety of 100/1000Base Ethernet
interfaces. They each also have one WS-X6704-10GE out
of which connections to our primary and secondary
backbones originate. This is how the routers are
interconnected.
Three of the five core routers are currently running
IS-IS. If we ssh into any router and ping
www.netbsd.org every other packet is lost.
At the end of the network are two 6506 switches each
with a 10GE module and a 1GE module.
Attached to the 1GE module are fiber links two
two different Juniper M10s which also run IS-IS
and through which we get upstream connectivity
to our provider.
All of our routers are level 2 routers in the same area.
Does this help? If not please let me know what else
you would need.
Thanks,Steve

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