Hi All:
O.K., after Jim's suggestions I decided to plunge in!
On Saturday I removed the gas tank (damn plastic replacement tanks!) and poured out the fuel; lots of "paint chips" from the interior coating of those old Jerry cans!
I rinsed the tank out three times until no more debris came out, then moved onto the carburator. I looked at the carb section in my 2F FSM and the diagrams did not mention any bowl drains; Not wanting to screw things-up, I just removed the feed and return lines and blasted them with carb cleaner. I also blasted the interior of the carb with the spray cleaner.
Well, I drove the rig up some steep hills yesterday and today and it seems to be running well, with no stumbling or hestitation. So, hopefully the issue has been dealt with! I will need to drive it some more to rule out any further issues.
It seems that perhaps these "paint chips" were getting sucked into the fuel system, and once the fuel demand got high enough, would clog the pump or carb?
Thanks everyone for their suggestions!
Alan