I'm getting high utilization alerts on a tunnel interface. It appears that Ciscoworks thinks the line is only capable of 1 Mb/s. That only thing that seems to make sense is that Ciscoworks is getting that line speed from the bandwidth parameter on the interface, although I've only ever used the bandwidth parameter for altering routing. Before I start altering that parameter I wanted to confirm that is indeed the case.
That is correct. SNMP gets the interface speed from the bandwidth statement. DFM uses ifSpeed in its utilization calculations. See this thread for more details: