Take a look at the Fuel Pump Drive Module under the truck at the rear.

Watch some You Tube Video on that.

While the Regulator is apparently a common failure on yours
I haven't found that to be true hardly ever on most vehicles.

Even if you resolve the issue,don't ride around with old spark plugs,
old O2 Sensors.

I find most all 5.4 have ignition coil failure,then the O2 & so goes the exhaust
converter from misfires.

You need to look a Scan Tool Data & be on top of all system items a couple times a year

Some vehicles you can drive for years & do nothing & others you can't & have one that you
need to understand & be on top off.