missing

I have a 71 dart w/318. The low end is great, very nice, very smooth. When going up a hill with no momentum, It starts missing and puffing smoke when the motor winds out. I will start at the hill and give it aggressive throttle to get up the hill at good speed ,this is when it starts missing. So under load is the main problem. Also, if I get on it on a flat surface, it goes, then in the higher rpm's, it starts the missing thing. I have replaced coil, electronic control module, ballast resistor, voltage regulator, holley 350 cfm carb. I was going to pull the plugs and see if any are showing signs of the misses. Any help appreciated!