1987 Ford F250 460cid Idle Misfire

Hey everyone, i have a 1987 Ford F-250 with a 460 Big Block W/ a 4 barrel carburetor. I notice that the truck has been having idle issues, it misses ONLY at idle, and its not a repetitive miss either, its random. I can floor it and the truck blazes tires but at idle it misses, i can put my hand over the exhaust and feel strong pulses of air when the engine misses. I’ve replaced the intake manifold gasket, changed the timing chain, got a new cap, rotor, plugs, plug wires, I’ve turned the idle mixture screws in until the engine started breaking up and i turned the needles back 1/4 turn, I’ve even rebuilt the carburetor to no avail. Lately i checked the voltage going to the ignition coil while the key is on and i only get about 6.5 volts. Is that my problem or is it something else? I was thinking of just running a jumper wire from the battery to the coil and run it on full 12 volts for a minute to see if its weak spark or something. What do you guys think? Thanks.