It dies while driving at road speed

Dirty posts start the problems...if it dies while driving the alternator or belt is not allowing the battery to charge...does it jump start OK?

Is the car warmed up or cold when this happens? Are you driving or sitting in park? Low speed or highway speed?

We need more info to help out. My best guess at this point and it's a longshot guess is throttle position sensor being faulty.

describe hayware.....is your charging system ok?

If the brake pedal goes hard right BEFORE the car dies, and not after, then you could have a problem INSIDE the brake power booster. try to verify this next time it dies at a stop, if you can safely pull the dead car off the road into a driveway (or try to make it stall in a bumpy parking lot) - then before you try to restart the car, open the hood, pull off the rubber hose where it's plugged into the brake power booster --> you SHOULD hear a big "Swoosh" of air being sucked into the booster because there's supposed to be a strong vacuum there even after the car stops running. if you get nothing there, your car is dying of an excessive vacuum leak through the brake booster.= bad booster.

Bad fuel pump.
If so,have to remove the fuel tank,to replace pump

sounds like a fuel problem, dirty fuel or blocked filter , there is another filter inside the tank attached to the fuel tap

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

Check to see if the serpentine belt is still on the car.

sounds like your crank sensor

my ram 50 starts just like any other vehicle, (no light switch pulling whatso ever), it sounds like somebody haas rewired something wrong or you have a loose connection and when you hit a large enough bump it cuts your power. Start it up and find a speed bump somewhere and drive over it enough to give your truck a jolt and see if it dies.