Your descriptions sounds like a problem I had when the Exhaust Gas Temperature sensor in the exhaust needed replacing. $25 You also might want to change out all of the relay switches under the dash over your left knee cap. Make sure all the breather hoses are soft and get a good seal, as the rock hard breather hoses on top of the engine no longer seal. See my thread on Rock Hard Breather Hoses. Make sure that the timing advance vacuum on the distributor still holds a vacuum when you suck on the inlet. Take apart the distributor if it is not an electronic distributor, and make sure all of the swing weights are not worn on their pivot, have grease on them and they swing properly. Make sure the distributor cap is not cracked. Verify that the engine problems do not occur only when you are running accessories. If accessories cause the engine problems then you need to change out your engine ground at it's left front connection to the frame, and also look for rock hard electrical wires running from your + positive battery terminal to the bottom side of the fusible link box as it loses it's ability to carry current.