Gorms,
I thought that I would update things- I still have a whistle, but it's only done it twice, and it was a different pitch. I thought that I had two different sounds. I found that the first cylinder from the front of the truck had an exhaust leak. I replaced the gasket, and although the original one was still intact, you could see where exhaust was blowing by. Being thin metal, I assume that it vibrated when exhaust was whizzing past it. So far, all noises are gone. To sum that up, I replaced both flexible hoses in the boost line from the intake manifold to the wastegate, and the exhaust manifold gasket.
Mark

Gorms,
I didn't know if you had followed my post, so I thought that I would drop you a PM. I replaced the short flexible hose from the AFC housing to the hard wastegate line, and my whistle is gone. I have run the truck hard for three days now, and it hasn't done it once. The old hose had no holes, but I think that once it warmed up and got pliable, it was letting boost pressure whistle past the hard metal line. Either putting a new line on, tightening the clamps, or more likely both, cured it. I like .25 cent fixes...
Blessings,
Mark