Hey Doc,
It means that your carb isn't getting enough fuel and here's why: When you backed up the hill, you forced the gas in the float bowl to the front of the bowl, Exactly where the jets are. When you are going up normally, the gas goes to the rear of the bowl, starving out the jets.
Where the fuel line enters the carb, there is what looks like a big nut, it's actually 1". The 5/8th fitting on the fuel line ties into it. Inside there should be a paper filter. I suspect that it's clogged and is the culprit.