Running rough when hot

[Chris in MA]

Hey all,
Took the 40 out today, runs smooth for about 15 minutes at speed then starts running rough. Stalled at an intersection, cranked fine, plenty of gas, no start. just spun.

Waited about 20 minutes, got it to start, ran smooth at idle/speed for a bit, after a few minutes began running rough again. Pulled over waited about a half hour and drove home. took it easy, but running rough at speed (~30 mph).

back story - just got the car back from the mechanic for a motor refresh recently, have had a few shorter drives, has a fresh Skips coil, rebuilt Bubba distributor, rebuilt carb, new wires. Mechanic said it ran rough with Skips coil. He replaced with NOS coil. I suspect he used the same condenser, but problem he described is similar prior to replacing coil.

If not coil, what else? Seems weird to me that a) Skips coil failed (I have not called him yet to check coil - non issue) AND NOS coil bad?

Your thoughts?

Thanks,
Chris