Hi
Do revert back how many links are getting terminated onto this router and the bandwidth capacities.
Also confirm whether CEF is enabled globally on this router..
You can try enabling ip route-cache flow under your lan interface and make use show ip cache flow to check what kinda traffic patterns are being processed by your router...
The output of this show command will give u the source/dest ip address as well as port numbers(hex) which you can easily decrypt and identify the root cause.
regds