I have been suffering from symptoms that indicate that my petcock may be failing. Specifically some strange stutters at 55-65mph.  Switching to prime seems to clear them up.  However, I have never found fuel in the vacuum line.  Also, I recently checked the petcock by doing the following:
1.  I unhooked the fuel line from the carb and put the line in an old glass to catch fuel. (petcock is in "on" position)
2.  pulled vacuum line from carb.
3.  Using childs medicine syringe, created vacuum  in line.
4. gas flows out of fuel line into cup.

So is the petcock failing?  or is the line collapsing under the vacuum.  I have screw down hose connectors so it is not the connection on the line.  Any ideas????

I would agree that your petcock is probably fine. However, a really cheap insurance policy is to spend a $1 and go to your local auto parts store and buy a foot of automotive vacuum line. Just swap it out with the stock line. The wall thickness is much greater and if you have a small split or crack in your OEM line it will solve the problem. Here is a comparison of the OEM line on the left and the automotive replacement vaccum line: