trouble shooting

I have a 1970 GMC Sierra 2500. With a 350 engine. 2wd. My problem is when I'm driving it will totally cut our like its either not getting gas or spark. If I let off the gas it will idle down and eventually start idling properly. Ususally when it seems like it catches it self I will push the gas again and it will sputter, do nothing, die or quit running, lunge, backfire......Sometimes it totally dies and won't want to start back up right away other times it fires right back up. Seems to run ok and get up to high forties sometimes even in the 50's with no problem when its cold. It will usually only cut out for the first time at higher speeds 40 and up. Unless going uphill. Once it cuts out it will do it on a regular basis hardly ever getting abouve 10-20mph. I have changed the fuel filter, pulled the filter out of the tank and checked and cleaned it. I also have repalced my cap, rotor, and plugs. When I first did this it ran great for like two days then it started to do the same thing again. I have been told it may be the float in the carb, also it may be the pickup coil, someone said points, some sort of a resistor. I'm really trying to get it figured out.