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If your truck is carborated then you will know if the ignition module goes because when it does it is just dead. it will just die or won't start. this is not you problem if carborated.
Check your distributor. Look to see if you have a TFI module mounted on the side of it. If so, buy a new one and get rid of the old one. FOrd has big problems with those TFI's overheating on the distributor and causing engine to stall.
I had many problems with the TFI module on my 85 Ranger I used to own. I think I replaced 2 or three of them. I think there may have been a recall after I got rid of mine, so you might want to check into that.
As far as diagnostics, I think you need an electronic diagnostic tool to be able to tell for sure if it's bad. But when mine went bad, symptoms were that first at higher speeds the engine started skipping, then idle went bad, and started stalling at low speeds. Finally it would just quit.
All in all, that was a horrible truck. It had the 2.8l V6 and I had nothing but problems with all the emissions valves and sensors. Much happier with my 96 4.0 XLT! (Knock on wood..)