I need help getting my truck dialed in

[1970heavychevy]

I have a 70' c10 but the motor is a 70' 350 out of an Impala. It has an Edelbrock #1405 carb. and Edelbrock intake. I bought it from my dad 2 years ago and he bought the motor rebuilt 3 years ago before that. So the motor was rebuilt 5 years ago. My dad ran it 2 years before it started acting up on him. The issue I'm having is.

The truck fires up with no problems and idles with no problems (it does have an aftermarket cam so we were told).
When I take off most of the time it runs great, lots of powers, gets a wheel in second (auto th350 trans). But when I get down the street a few miles everything seams to bog down and I have no power and have to limp home.
I have replaced all the fuel lines and filters. Replaced the fuel pump and installed a regulator. I have cleaned out the carb.

What next? I am frazzled!