WE'VE HAD THIS TRUCK BACK TWO TIMES. IT HAS GAS, GOOD BATTERY, GOOD SPARK BUT WON'T FIRE BECAUSE THE DISTRIBUTOR SHAFT KEEPS SHEARING OFF THE ROLL PIN KEEPER ON THE LOWER HALF GOING TO THE GEAR AT THE BOTTOM OF THE DISTRIBUTOR SHAFT.

Sounds like timming to me?

Check temp sensor and TPS, throttle positioning sensor.The power control module,"pcm.is a possible thought.Just check all connections. It is always a good idea to spray WD 40 or equivalent in the connections.

If you have spark at the right time, compression, and fuel, you should have combustion.
Was it running before you had the work done ?
Is it possible the distributor timing is off ?
You know for sure the plugs are firing, not just the coil ? And the accel pump in the carb is spraying gas ? And the choke is closed ?
A major vac leak like the PCV valve hose or intake gasket could keep it from starting.

How do you know the battery is good had enough crank power?

Inside or directly under the distribitor cap is a plastic ring with either one or two wires attached..... these devices fail and not allow the engine to start.
It happened on my 88 chevy (305 cu in.). a quick fix is to replace it with a new one.. (Advance Auto) or other parts store.

you said you repl dist cap that means you don't have a crank sensor you have electronic ing module. remove your elec ing module have it tested most auto parts stores could test your module, or check your coil at the neg terminal. should have power. if not you lost your primary volt from your batt.your secondary power is coming from your electronic ing module from the module to the pos terminal on the coil, when the eng cranks,from the coil to the dist cap , from the dist cap center to the rotor then out to the plugs,this all happen pervided the timing belt or timing chain is ok. the cumbustion chainber needs 3 things , thats fuel, air, and spark.

Possibly a sheared roll pin on the distributor or the gear is striped. Take the Distributor cap off with wires attached if there is room to move it out of the way. There should be a bolt at the bottom with a bracket, remove the bolt and bracket and remove the distributor, check the roll pin and gear to make srure there in proper condition. Both ends of the roll pin can be there but still sheared. Check also but hold the rotor button and turning the gear to make sure that the shaft is not broken. Gear is at the bottom.

Something has sheared. Is there a pin on the distributor drive gear, are the gears on the cam and dist. shaft perfect / no flat spots at all, is there a keyway or key on the crank or cam gears that has sheared? Must be a weak point that was slipping somewhere.

Have you checked your connection to the battery? Sometimes a bad connection can drain the battery and keep the alternator from returning enough charge to the battery.

The mechanic should check on the distributor assembly and the spark plug ,spark plug cable. You should set first the distributor shaft rotate it counter clock wise or clock wise . according to the way you will set the spark plug to connect on the distributor assembly. If the timing will be 1342 there for the timing on the shaft should be set at the 1st spark plug and spark plug cable. When you hit the gas pedal it will back fire because of the distributor assembly and the spark plug is not set on timing or proper timing for compression.