93 Pickup stumbling bad, different from other stumbling problems
 

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Did you get all the plug wires (and coil wire too) fully seated in their respective terminals?
Did you get the intake ducts installed properly, with sufficiently tightened clamps?

Considering the fluctuating idle speed, I would thoroughly check for vacuum leaks and also check the throttle position sensor operation. If it's not working properly, it could cause the ECU to use the oxygen sensor for mixture control at idle, which it shouldn't be doing. And if the TPS is causing this, it will also be very difficult to get the timing set properly since if the TPS isn't working properly the ECU will not go in to the proper mode to set the timing correctly.

For future reference, all you need to do to set the timing is start the engine and warm it up completely, then jumper the diagnostic connector while verifying either (a) the idle speed changes when you put the jumper in (if it doesn't, the TPS may not be set properly) or (b) if you have your timing light ready to use you can check the timing mark before and after you insert the jumper: should be off the left side of the scale (and may be jumping around a bit) by the pulley without the jumper inserted, then shift to the right (and stabilize the position) when the jumper is inserted. If the idle doesn't change and/or the timing marks didn't stabilize with the jumper, check the TPS operation.
After that's settled, adjust the timing, readjusting the idle if necessary.

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You said in your first post that you tried changing the plugs and wires and put your old distributor cap back on... so I assumed you changed the plugs and wires. ;)
That's why I asked if you were sure the wires were fully seated.
Don't want to be chappin your hide here, but you can't say you did something, like changing wires, cap, rotor, etc. then say you didn't touch them. Catch my drift? You can't say you have all new wires and then say the only wire that was touched was the coil wire.

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Okay. Although you said in your first post that you removed the distributor so you could get to the alternator ... which means you'd have to remove the coil and plug wires... I'll let that go.
Consider it
bridge
water
(water under the bridge ;))

without much else to go with, sounds like your timing may be off. I gave you some 411 to help you get the timing set properly in my first reply.

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I'm not saying you're BS'ing. Please don't take it that way.
Ambiguity doesn't help us help you figure out the problem though.

But I will stress that idle and timing must be set with the engine warmed up, regardless of how it runs cold.

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If coil HT (secondary) voltage is too high and arcing through the lead, the coil primary resistance might be too low.

The distributor only passes a low-volt signal (hall-effect) to the igniter which in turn switches the coil primary circuit like points did for older vehicles.

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It could indicate a grounding issue. You've checked the engine block and cylinder head ground leads, no?

But have you checked the coil primary and secondary resistances to make sure they are within FSM specifications?

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There should be a ground lead from the rear of the cylinder head to the firewall as well.

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