How much memory do you have in your server.

I dont believe dbcc perfmon will give an accurate cache hit ratio in configurations where AWE is enabled.

Have tried monitoring the server the performance monitor using the specific sql objects? I wouldn't advise running this continually it eats resources.

If you need a cheap and easy monitoring tool try sqlcheck it's free and works fine.

If you're not using above 4gb of ram then beats me unless you've got the max memory set to some really low value.

Dave