I had a similar situation as you I had to read the FAQ and a lot of posts to find complaints similar to mine and see what fixes worked for them then deduce with my limited knowledge what would be worthwhile to try. I did all of them that would be necessary maintenance at 140K even if it were running good. That left me with a code I think it was, sorry do not recall, led me to change the dist pickup. Then I was still not happy I think it was even after I got a rebuilt trans so I added the Crank Sensor and that made it better. All of the new parts made it better, I just kept going until I started getting what I wanted. Turns out the guy I bought it from wasn't doing the maintenance like the original owner he bought it from did.
The Crank seems like it had more to do with shifting (auto trans) which was my main issue more than anything else. Your issue sounds a lot like Smokin1994 and a few others I have read that is why I think these two things might do the trick. It could still be one of the other sensors but honestly at that age they probably need changing anyway. They are all pretty cheap too. There is also a splice in the wiring harness under the box with the relays in it that gets corroded which can also cause intermittent issues. Try to digest the FAQ as best you can. there is a lot of good info there.

 

Honestly I do not know anything about the FAQ. And I agree the best thing to do is to replace all three high probability parts (cam sensor, ignition, crank sensor). I fret the crankshaft sensor because it just looks like a PITA. Not that I don't think I can do it but I just hate repairs like that. The contorting, working blind, etc.. I'm not 20 anymore and that thing is buried. I wonder what a dealer would charge to replace that thing. I'm guess a few hundred bucks.

Well, for now I can deal with the cam sensor and ignition. Those are easy. And I also agree that at 25 years old even if I replace parts that don't need replacing it likely isn't going to be long and I would have to replace them anyway. I kind of do that now with that truck with things like hoses, oxygen sensor, relays, etc... It is in great shape (only owner) and I always took care of it. Only 173,000 miles. And still the original exhaust system!

Anyway, thanks again for your input. It has been very valuable.

 

On the front page of the 1st gen sub forum there is a group of sticky threads at the top just over the Normal Threads. The first Frequently Asked Questions (FAQ) section is what you want to review. I spent the money because it had 140k miles, no rust and cost me $900 to buy. You have to decide what the value is to yourself.
Original exhaust. You may have a clogged Catalytic Converter. That too will caused stalls 'for no reason" among other problems.

I did the crank sensor on my 3.9L from on top. It was hard and I scraped the crap out of the back of my left hand against the heat shields on the fire wall. if you try that take the heat shield off. To do it again I would prop it on jack stands and take the wheel off and go at it from below.

 

Yes, after watching some vids it became clear the best way to get to the crank sensor was thru the wheel well. Even then it didn't look like much fun. Have to take all the wheel well liners off and it still looked tight. Have to get the correct size allen wrench and saw it down to get some clearance, etc.. Still working blind to a degree.

Don't want to think about a cat converter. Ugh!! That there have been a couple occasions where I had to wait 20 minutes for it to fire up again kind of sways me away from thinking its the cat converter. But who knows. I could keep going around changing stuff out until I get to the back seat and still not solve the problem. Best solution might be to rob a bank and buy a new truck. Might have to rob a few banks with the price of new trucks these days.

 

Did you try the coil when it will not start? Disconnect the connection, hold close to the connector and look for spark when starting.

 

Unfortunately, every time I was stalled there was no one around to help. However, I did change out the coil when I tuned up my truck last week.

 

I had the same problem.

 

OK, I changed out both the crankshaft positioning sensor and camshaft positioning sensor. Turns out doing both at the same time is the better approach because you need to remove the distributor cap anyway to gain room to access the plugs for both parts. This was not a fun repair. Very little room to work with so one handed and blind techniques were heavily employed. I opted to go through the right-front wheel well (as opposed from above) to get to the crankshaft sensor. That meant removing the wheel well liner. Also had to be creative with removing/re-tightening some fasteners. This is an ungratifying repair because it doesn't make my truck run better and I don't know if it solved my problem. Only time will tell. I noticed my RPMs reduced. Truthfully, I don't know what the spec RPM is for my truck.

Here is a vid on how to access the crankshaft sensor.

 

Saved some dough no doubt

 

No doubt. And the ONLY reason I did it myself.