Electrical driveability nightmare

I have a 1985 Chevrolet S-10, 2WD, 2.8L V6, California, 5 Sp Trans and oem prom and ignition system. The problem I'm having is directly electrical but I can't seem to nail it down despite the fact that I'm a mechanic myself. Unfortunately this electrical nightmare has eluded me. What happens is that it runs fine when parked or when driving as long as nothing electrical is functioning or being used. The minute I draw any current by using the headlights, brakelights, reverse lights, cigarette lighter, turn signals, stereo or any other electrical component, it starts running badly and/or misfiring. Depending upon the amount of current draw the problem is worse. For example, when using turn signals it only slightly misfires/drops idle speed and only occasionally will die. If I turn the headlights on however it dies every time I allow the engine to drop rpm to idle speed and usually won't even drive under it's own power due to misfiring so badly. I've checked output on the alternator and even replaced it just to eliminate the basics and same with the battery. I've checked all the obvious ground locations and searched for any apparent shorts to ground but have come up with nothing. I've talked with several other technicians in and around my area and none of them have any idea what it could be. If anybody has encountered a similar problem or has an idea of what it could be, please let me know. Thanks.

hows your coil?

hows your coil?

The coil, ignition module, spark plugs, wires, cap, rotor and ignition pickkup are all new. As I said, when nothing electrical is drawing amperage it runs fine, which it likely wouldn't were it the fault of an actual ignition system component. But in any event, the coil is good.

weird one.

I'd almost think that you have a bad ground still. Possible an almost burnt out ground wire, but if that were the case your starter just shouldn't turn over

You might want to clean the paint off the coil braket, and where it mounts too. That helped my 85 run better.

How did you check the grounds??? what was the ground drop reading?? Shorts to ground would blow a fuse. Look for bad wires at or near the fuse box.
It seems that any load that you add pulls power from the ign system I would do high load ground drop tests and then check all wiring for that green gunk stuff like on the starter, fuse box and ign switch. also check the battery cables, there might be high resistense in the battery cables

Do a voltage drop on the ground cable between the battery and the engine..anything over .5 volts while the engine is running is an indication of a bad ground.