B2600i Quits when it's warmed up???

I'm running out of ideas on my '93 B2600i.
It completely quit and I gave up on it for a few months. I'm now needing a vehicle (besides my '81 chevy 1 ton) so I've drug the old mazda back out. I just had the computer rebuilt, which fixed a lot of my problems, I also replaced the PCV valve/vent and grommet since the old one was falling apart. The distributor was also replaced due to broken off screws in it, also replaced coil, plugs, plug wires, fuel filter and the previous owner replaced the injectors. The pickup has great fuel pressure and spark. It is also perfectly in time.
The pickup fires right up with no hesitation (even when it's cold out) and it runs for 5 to 10 minutes with out missing a beat!. As soon as the thermostat opens and the top radiator hose starts getting warm the pickup misses out a couple of times and then quits. There is no smoke or anything out of the ordinary. When I try to restart the pickup it fires and tries to start but it "can't keep up". When I let off of the key and try again it then doesn't even fire???. When the pickup sits and is completely cold, it does the whole thing all over again.

I'm thinking it might be the Coolant Temperature Sensor, I watched a youtube video on how to check them with a volt meter, so I'm going back to the shop tomorrow to test it.

Does anyone have any ideas on what this could be?

I have a couple friends that are good mechanics and they don't know what it could be?.
Thanks for any info

Ignition coil? Alot of ignition components will start to fail when they get warm, then work fine when cold. It also takes less energy to spark at atmospheric pressure than compression pressure.

Coolant temp sensor is a good place to look, as well as the air temp sensor in the front of the intake.

I've had issues with the MAF sensor plug where the wires go into it.......cleaned them and it worked fine after that.........could still be a ECU issue also. Several others have had their ECU rebuilt and had problems with it again shortly there after.

Have you connected a timing light to verify that it is not getting spark when this starts to happen? It could be a fuel issue instead of spark.

Thanks for the info, this is a fuel issue not a spark issue. It does fire on starting fluid but it will not run.
I'm getting ready to go out and test the Coolant temp sensor and I will also see if I can test air temp sensor while I'm at it.
I'll keep everyone updated
Thanks again for the info

Check your fuel pressure when it is happening, see if it is a fuel delivery issue or fuel injectors not firing.

I already checked fuel pressure and it is really good, the injectors are also firing.

I tested the Coolant temp sensor and it should test at 2 ohms and it tested at less then 1 ohm. So I'm going to order the part and see if that fixes it.

Thanks again for the tips and info

Thanks for the links,

I checked the O2 sensor today and I believe it is bad. Would this be causing my problem? or does this not really matter? I'm going to try to read code with a volt meter and see what happens. I'm really running out of ideas and I'm getting tired of this pickup!.
Thanks again

Really now that I think of it, this pickup quits before it's warmed up, it ran today for 40 seconds and then it quit like the key was turned off. There was no smoke, smells, or anything else. Just shuts off and it doesn't even sputter.

Have you verified that your ignition switch is not the culprit? They are notoriously bad in these trucks, the electrical part stops working. I think you can give it a jiggle to make it work again. Might be loosing power to the ECM randomly?