Why does my truck die when I put the clutch in?

4 turns? Holy. It was almost all the way out. Full revolutions? You need to feel and listen to the engine as you're adjusting the mixture. Old school way to adjust is to turn the idle speed down some, and thread the mixture screw in until the engine begins to stumble. Then back off one quarter revolution. Then readjust the idle speed.

My pleasure.

High idle? Turn down the idle speed.
Is 3 turns out the lowest amount before the engine begins to stumble? It should be turned in until the engine begins to stumble and then turned out one quarter revolution.

That is weird. The engine should die when the idle mixture screw is screwed in all the way. It's supposed to shut the supply of fuel off at idle. Or very close to off.

So where are we now? We've adjusted the idle mix pretty close to exactly where it should be. But the idle is still high. Have you turned down the idle speed yet? The one on the throttle linkage side. Once you get it into the right engine speed range, check and adjust the timing.

Preferably you would have a timing light. Turn the engine until you can see the mark on the crank pulley and mark it. Remove the vacuum line from the distributor and plug it.
Loosen the bolt on the distributor hold down. Clamp the magnetic pickup to #1 plug wire and power leads to the battery. Point the timing light at the crank pulley. Look for the mark on the crank pulley and read the timing scale. Timing should be 8 degrees. Once you have it set, re-tighten the distributor hold down bolt.

Same process.

I'll be here.