IME there are very few things that are "standard" practice among GPs for most conditions or diagnosis. They each tend to operate from the base of their own training and experience. What resources they are aware of and familiar with in the area, and if they are in an HMO, what the plan will pay for.
Very often it IS up to the patient to keep pushing, searching etc. at least for the appropriate tests etc to establish an appropriate diagnosis. Many drs operate more from "symptoms" rather than diagnosis supported by a battery of tests, if they feel sure they know what the issue is.
Sometimes a younger dr, just out of training, has more familiarity with newer ideas and tests. Sometimes you can find someone who has done a residency in just such a program and is eager to apply what they know.
Do you have an teaching hospitals in your area, perhaps one associated with a local med school?