Got a 2004 F250 superduty 6.0 powerstroke. Guy before me ran it out of fuel, refilled it, but couldn't get it started. I primed it and got it running. Problem is it won't go anywhere unless you are spraying starter fluid in the motor. Changed the batteries and fuel filters. Has some trouble starting up without the starter fluid, but once it's running, it revs up fine. Don't think it's the trans since it does move with the starter fluid. No blow by or check engine light. I'm looking at a fuel pump, regulator, pressure sensor, or injectors. Where should I start?
EDIT: It was the HPOP

 

The fuel pickup tube in the fuel tank is known to break as the plastic ages. That typically shows itself when the tank levels get low (around 1/4 tank) due to the most common place to fail being the "vacuum breaking valve" on the side of the pickup tube near the bottom foot. That said, the tube has broken at higher points for some folks. Plastic bits can get drawn into the fuel lines and cause issues as well.

To inspect the pickup tube, the tank has to be dropped, or the bed has to be raised.

As far as fuel pumps go, a member of another forum tried tracking down a common mileage point for the original fuel pump to fail. IIRC he saw it to be most common around 200k miles. Generally those OEM pumps are pretty good, but after a lot of miles, they can/will fail. When mine began failing, I saw it as low fuel pressure (I constantly monitor fuel pressure since low fuel -pressure can ruin our injectors - and they are expensive). Every 6.0L owner should watch fuel pressure since Ford identified low fuel pressure as the number 1 cause of injector failure.

Using aftermarket fuel filters can also be an issue. Many aftermarket brands do not fully open up the pump inlet path or allow flow past the secondary filter.