I am currently taking 20 mg simvastatin for chloresterol. I have had a second dr. Tell me that was a very high level. Is this a unusualy large dose?

No. 20 mg is an average dose for simvastatin. If it is controlling your cholesterol levels and you're not having muscle cramps or elevated liver enzymes, there is no need to lower the dose. If you are having problems, see your doc for blood tests for the liver and muscle; if they are significantly elevated, he may stop the med/lower the dose/ change to different statin/try different med family.
Simvastatin. That drug comes in 10, 20, 40, and 80 mg tablets. Dosage adjustment of medications depends on whether or not the person treated has reached goal of therapy.