Truck stalls when driving in town or freeway with no warning cold or warm. i have replaced the ignition coil, computer, m.a.p.sensor, cat converter

Check the plugs at the coil and ignition module. You can grab them and wiggle them also. if it acts like it wants to stall, fix or replace the plug.

No, not the oxygen sensor. A couple of things you need to make clear. What light flickers, then stays on? That can't be a sensor light, it would have to be the "check engine light" or an engine temperature light (for like when your cluster has no temperature gauge, but just the "red light").
At any rate, the sensor you changed is not the engine temp. sending unit for the instrument panel. I believe on your '89 there would be two sensors for temp. One is the CTS for the engine computer, and the other is a sending unit for the dash, probably a 1 wire connector. It could be at fault, but it wouldn't cause stalling, I do not think anyway.
If it stalls and won't restart until cooled, this is a symptom of loss of ignition (spark) caused by either a faulty coil, or faulty Ignition Control Module (the coil controller), or last a faulty Crank Position Sensor (this sensor used by computer to determine ignition spark timing). You could test if ignition is lost, by checking for spark right after the engine warms and then stalls. If you have no spark to a spark plug right after it stalls, this is the reason for stalling. Usually it is the crank sensor, rather than the ignition control module or an ignition coil. Your car has 3 coils anyway in a "coil pack", so if one coil went bad, you'd still have two good coils, but engine would only be firing on four of the six cylinders-could easily stall a car.
You should check for trouble codes whenever you have a problem. A code might have been set. Easy to check for codes on your car, just ask if you don't know how-only takes a jumper wire or even a paper clip works. good luck.

check for codes then you will have to check fuel pressure/volume, ignition system for worn parts. you may have an intermittent sensor problem.

check for a fuel flow problem( pump pressure-filter blockage-injector/s) run fault codes ( check for HO2S and O2S sensor operation.. Check cat converter is serviceable Blocking exhaust system

I was just thinking about the sudden stall problem ,and no start problem .Have you checked the coil pack. When the car is cold it should start ,when it warms up ,with the under hood temps ,it will probably stall ,again. Try replacing the coil pack .
Hope this helps

probly camchaft sensor

sounds like you are dealing with either a bad crankshaft sensor in ignition coil(s)

the thermostst is most likly stuck in the open position letting the coolant flow freely through the engine and keep recuirculating not giving it a chance to stay in the engine block to warm up. i would replace the thermostat

Guessing gets expensive. Is the check engine lamp ON? If so, there will be stored trouble codes that are necessary to propely determine the cause of the stall. Catalytic converters do not unplug when cold, if they are plugged, they are plugged at all temps and vehicle runs worse the more gas you give it but may idle OK. Typically, stalls after warm are electrical failures, often computers, or solid state components that fail when they heat, and cool off over tyme. Ignition components are highly suspect generally, as are sensors. crankshaft position sensor especially is common to fail only warm on most vehicles.

Try checking the exhaust flow when someone else is pushing down on the gas petal.The farther the petal gos down,the more exhaust should be coming out. I replaced my catalitic convertor at 44000 miles, it was clogged. I had them install a high flow type.