Back in the old days, Model-T's used to have this problem...they didn't use fuel pumps...they used a down draft system (gravity) which located the gas tank right above the driver's lap. But if you were traveling up steep grade, no fuel would reach the carb. The solution for this was to turn around and back up the hill. Crazy!
Your problem is the float setting in your carb. On an upward incline, the fuel is pulled to the rear of the float bowl...the float "says" everything is fine, yet the the jets are thirsty.
Have whoever rebuilt your carb do a better job measuring the float setting.