Car starts and runs for a while then shuts off while running. What could be wrong?

Could be hooked up wrong or not at all. If its getting gas at the engine, might be a clogged line. did you have the fuel filter replaced to.. ? check it. But first CHECK IT HAS GAS IN IT !!!!! Not by the gauge. Put new gas in it...... Good Luck

If the fuel pump(s) run while the pressure is falling, replace the fuel pressure regulator and (although I'm sure you've already done this), replace the fuel filter. If the fuel pumps appear to be turning off by themselves, replace the inertia (fuel cutoff) switch.

If the pump continued to run after shutting off the car you fuel pump relay was probably staying latched. I would replace the relay as well based on your info. Along with the pump the fuel filter should be replaced too and fuel pressure should be checked. Make sure your ground is good also.

No the missing O2 sensors would not keep it from running. The missing exhaust pipes might not help matters. No exhaust system would cause a lack of back pressure.
I would want to know what base fuel pressure is with a gauge before and after cranking. Your thought about bad gas is legit, today's gasoline is only good for about 2 or 3 months before it starts gelling up.
Did you replace the inline filter the last time you put the new pump in ? And are you sure the pump is getting power after the key is released?

You can put a pressure gas on the fuel line and check the pressure from the pump and see if it is running and then shutting off intermittently . I would also change the fuel filter if you have not done so already.

sounds like you hooked the hoses up wrong at the pump unit or you have a bad fuel filter...replace the filter first..then check those hoses and clamps.

If you hear the fuel pump come on when you put the key to the run position...then replace the crankshaft position sensor, I would also replace the camshaft position sensor as well because a failure there will have the same effect, and its cheap insurance against further breakdown. $80 for both at rockauto.com

When the crankshaft position sensor fails the engine will run for one second then shut off as if it ran out of gas.

Make sure your fuel pump is running; it should run about 5 seconds when you try to start the car. if not check the fuse and relay for the pump and the ground strap

Make sure your battery is in good condition with tight connections.

IVE HAD PLENTY OF THESE GO OUT EVEN A MONTH LATER. AS FAR AS THE STARTING FLUID JUST TRY AND CYCLE KEY BUT KEEP IT FROM TURNING STATER OVER. TURN ON AND OFF ABOUT 3 TO 5 TIMES IT SHOULD BUILD ENOUGH PRESSURE TO START. TO START MINIMUN PRESS IS 55PSI.

1. Does the pump actually run (key on engine off) pump should run for 2 seconds and go off and can be heard if you listen at the filler neck with the gas cap removed)
pump not running - Check relay (replace if bad) check wiring/fusese

Pump runs... go on to #2...

2. check the gas guage. is the gauge reading in the normal area it would read in or is it way way off like WAY above full or way below empty? This is a sign the electrical connection at the pump is plugged in backwards and the pump is spinning the wrong way and not picking up the fuel... (This is easy to get plugged in backwards inside the tank when installing the new pump)

3. Check for feed, return and vent lines being installed wrong where they attach to the tank... they can easily be hooked up wrong and fuel is either pumped up in to the return line or pumped in to the fuel tank vent line..

4. check for kinked or crushed fuel lines from tank to engine.

5. check fuel pressure regulator to be sure its not stuck open.

I see you say that you have a new fuel filter but did you try replacing the fuel pump??? If not you can check the fuel pump simply by turning the key to the ACC position (thats as far as you can turn the key WITHOUT starting the truck) listen by where you pump the gas in and try to hear a low sounding whine if you cant hear it then it could be your fuel pump is dead and needs a new one....or it might be going dead.