2001 5.3 260kkk miles. After it warms up completely, it will stall at low idle, especially when put into reverse. Had a misfire on 4. Changed the plugs and wires which fixed the issue of it bucking while light acceleration while driving. Removed and cleaned the throttle body, idle air valve, egr valve, maf, new fuel filter. Have owned the truck since 2002, and have replaced the fuel pump twice, alternator once, and recently a rebuild transmission. The truck will flat out scream until it warms up and is idling in gear. Also a new thermostat because I was getting cold.
Also not any codes yet.

 

Check the fuel pump pressure as well as the operation and integrity of the fuel pressure regulator.

 

I had an similar issue with my 2000s. Try replacing the intake gaskets, thats what fixed mine

 

I hooked up the pressure gauge when the truck was warmed up and stalling. Gauge read 52 when I turned the key. After starting, the gauge went to 48 and held there after I shut the truck off.
somehow I ended up with 2 accounts but this is Jason

 

Well, the factory spec for the fuel pump pressure is 55 - 62 PSI. You mentioned that you have replaced the fuel pump twice. What brand(s) of fuel pump did you use and how long did each last (time and mileage if possible)?

If you did not use either an ACDelco or a Delphi fuel pump, you could be looking at another defective fuel pump.