The Code is PO401, there are no other codes. The engine is a 4.6L, and has 120,000 miles on it. There has been no performance issues since I got the Check Engine Light.
I took the EGR Valve out, it had a light dusting of light grey soot in it. I held it upright and Sprayed the Valve with Carb. cleaner, while applying vacuum to it. Valve opens and closes with ease, and the Diaphram holds a vacuum. Caught the Carb. cleaner, it was barely grey. Port to the intake is clear. EGR tube seems to be clear using a screw driver in it.
Reinstalled, reset code, it came back.
Checked EGR Vacuum regulator, it's at 33.8 ohms. Harness has 11.84 VDC on it. Battery out is 12.53 VDC.
Differential Pressure Feedback (DPFE) with ignition on, engine not running, Haynes says 4.0 to 6.0 VDC. Haynes Manual says to check it with Engine running, and the cold range is 0.02 to 0.07 VDC. Engine warm, range is 4.0 VDC to 6.0 VDC, but doesn't tell you which harness pins to check across. IE Right to Left "Left = Drivers Side"

Where do I go from here?

Updated, wasn't checking correct control for 4.0 t0 6.0 VDC

 

Your static testing has it's place however it failed to pick out the cause of the 401 code.
Here is a better way to test.
With engine at idle pull some vacuum on the EGR and observe the engine idle quality.
If it goes rough, you know the path from the exhaust manifold through the EGR and through the intake manifold is clear by the reaction.
This leaves the DPFE and possibly the EVR solenoid for fault.
The DPFE has to be able to dynamically measure the pressure drop across a small orfice in the metal tube. If the DPFE is corroded, blocked or just is faulty, you can't tell with a voltage measurement.
If the first test causes engine reaction, the DPFE likely needs replacement with a FORD part not an aftermarket unit.
EVR: It's a 3 port device. The third port is actually under the round cap. Under the cap is a filter to clean the small amount of air it lets in to allow the EGR to close once it was opened by vacuum.
With this info you should be able to narrow the issue down.
Good luck.

 

I cleaned the EVR filter, checked the EGR valve with a MightyVac pump, engine did stumble. Also I hooked a vacuum gauge to the hose for the EVR valve, and mildly accelerated up and down my long driveway, and I get a change in vacuum. Tried to get the DPFE off, couldn't budge the hoses. Are they special material, as I noticed the inside layer of one is Orange?

Got to be careful I don't strand myself. In two weeks our work yearly budget ends and this week is when they make their very final decision of who they keep, in the new fiscal year.

 

I replaced the DPFE-4, it's been driven 40 miles since then with no reaccuring code. Everything else tested out, but I couldn't test that device. Dealer wanted $100 to pinpoint what was wrong. I think I could have replaced everything in the EGR system, plus the part they found bad, for that price.

I couldn't find the high temperature silicon 1/4" and 5/16" hose, that connects them to the EGR pipe.

 

Good you got the trouble.
The hoses are two different sizes so about any good hose will work as long as they seal at the metal pipe and on the DPFE.
NOTE: If you can't get the hoses for awhile, and have a code as a result, it won't disable using the truck.
The DPFE is only a test device to check the integraty of the EGR system as demanded by the EPA for the truck to be legal to market so it meets min Emission standards for NX output.
The only result of it not working is a drop in fuel mileage.
That's another explanation of how and why.
Good luck.