So I cleaned out the petcock, fuel's flowing freely from there. What I now believe the problem to be is that the tube running from the petcock to the carb is crimped. It looks like it wasn't long enough when it was installed (I don't think it's the original because it has a filter on it) and it's crimped where it had to bend up to the petcock. Fuel goes through it but it may be causing enough blockage to bog it down at faster speeds. Since it's been that way for probably at least a decade I can't get the crimp out completely.
I'm going to look for a new one at a few motorcycle shops around here Monday and see if that solves the problem. If not, it's back to the drawing board.
This is just something else that may help identify a cause for the bogging. I've been able to get the bike to full throttle while on its stand if I ease into it really slow. If I give it full throttle right away it bogs. With me on it (I weigh all of 145 pounds) I can't get it to full throttle at all. Hope that helps.