I still see it in the .png as much as I see it in the .tif. I've run it through a few different players. And not to sound condescending, but I think Adob'es mercury engine decodes AVCHD just a little bit better than Vegas. Nevertheless your insight is helpful. I've noticed less artifacts the now that I've hooked up my monitor to HDMI. It has issues, but it's not critical enough to warrant any returns.
It's interesting, I have noticed this with HDMI as well. There is really something to be said for how things are monitored. When I booted into OSX for some reason those gradation "artifacts" were more obvious, but on Win 7 the footage looks fine. Just another thing to be aware of when it comes to AVC footage.