318 Runs Crappy at low speeds when hot.

Hello Everyone, my barracuda all summer has been falling on its face once it heats up to full temp. (180ish) Its a 318 with mild cam/headers, holley double pumper...All new autolite plugs, MSD wires etc. I can take off and the thing runs sweet out of the gate, will cruise awesome all day at 45+ MPH, but once I start hitting towns and running into stop signs etc it has a nasty miss, it feels similar to if a spark plug wire is loose etc... Sometimes if i put my boot into it and let it kickdown it will run run fine again when i get to my highway speed driving. Any Ideas on where to look? Is it possible my ignition box is taking a crap when it gets warm?

Thanks,
Brad