It sounds to me that you are experiencing ignition miss. This could be created from a wide variety of problems. The 350 motors often had oil consumption problems that led to plug fouling. The first thing I would suggest is that you have the ignition scope tested. If you are approaching this as a do-it yourself situation I would read your spark plugs. They should be an even toast brown with very little buildup of ash or soot. If these look reasonable then I would try misting your ignition wires, cap and coil with a spray bottle filled with water. This would be best viewed in the dark, of course the engine must be running.I hope this helps and heads you in the right direction.