WAN killer does not work with tcp echo option, and Cisco router "tcp small servers" parameter set, so data can not be wrapped back . Only udp echo works.
Is your router configured for echo?
I have the "service tcp-small-servers" parameter set. Is there another parameter that should be set?
Have you verified that the router is actually echoing tcp by testing it manually? Is there any kind of firewall that might be between the device hosting WAN Killer and the router?
--HTH
Steve