Cuts out going up hill.

My 67 Dart I can drive around town and on the freeway at speed just fine but when i got up a decently steep hill going 45 or faster the car will start to stumble like its losing fuel. When I step on the throttle i get nothing and i have to feather it until i get to the top and back on flat road. I stopped and the filter is full of fuel can hit the gas normal and the car seems fine get going back down the road and no stumbles can hit the gas hard it dosent fall on its face. Only when i go up hills. It has a 318 stock, 750 edelbrock carburetor and i have a holley mechanical fuel pump that has a higher gph then the stock pumps. Ive had this issue with stock pumps to. Only thing i havent checked is the sending unit I put a brand new tank in it a couple years ago with a new sending unit. Like when the fuel sloshes away from the pick up when going up hill my tank was full when it happend. Anyone els had an issue like this or other stuff i should check. I starting to lean to changing it over to and electric fuel pump and a tank with a pick up on the bottom of the tank.