I'm guessing you're talking about GRE tunnels. The default bandwidth figure assigned to a GRE tunnel interface when it's created is 9kbps. This is the figure the SNMP agent returns when asked what the maximum bandwidth of the interface is. Do a "show int" and see the BW figure around the third line. Adjust this to something more realistic for the tunnel. e.g. 2Mbps

interface Tunnel99

bandwidth 2000

This can be difficult but I use the max bandwidth of the smallest link in the tunnel's path... if you know what it is. Otherwise just try and make a reasonable guess of the max throughput the you think the tunnel could get to.