1997 F-150 P0401 EGR Code

So here's the Story so far.....

1997 Ford F-150 XLT Supercab 4WD
4.6 W
R470W Auto Trans
192,500 Miles.

I keep getting a P0401 Code "Insufficient EGR Flow"

Here's what I've done to try to solve the problem.

1. Replaced DPFE
2. Replaced EGR regulator
3. Pulled and checked the stainless tube from header to EGR valve
4. Pulled EGR valve and checked for operation with vacuum pump
5. Pulled vacuum on EGR valve when running, reduced idle speed and "stumbled".
6. Pulled vacuum container from behind battery box and it tests airtight.
7. Pulled the big connector off the PCM and sprayed the contacts with contact cleaner.
8. Checked the integrity of all involved vacuum hoses.
9. Made sure the Throttle body ports were clear.

Today, I put a vacuum gage inline with the EGR valve to watch it while driving. Also, I put a voltmeter on the Brown/Pink Stripe wire to the EGR regulator to watch while driving.

Here's what I saw. (assume thetruck (http://www.ford-trucks.com/advertiser/kwldirect.php?kwid=528)is at operating temperature)

1. When the truck is started, the voltage goes to line voltage ~~13.4 volts.
2. When the throttle is depressed, IF the voltage drops, the vacuum goes up (and I assume the EGR valve opens).
3. When coming to a stop or the throttle is fully released as in coming to a stop, the voltage goes to max, and the vacuum goes to Zero.
On most test drives today (probably 10) at least once or twice it just stops responding to the throttle. Stopping the truck, turning it off and restarting seems to clear the problem for a few miles.
I really need to get this fixed as I have to get it emission tested next week for my new tag.

Thanks for any help anyone here can offer.

I had a friend with a 1997 and his problem was the inlet to the egr valve was plugged. He started with a 1/8 then 1/4 then 3/8 and finally a 7/16 inch bit.
Normally you can use a screwdriver and ream out the hole then blow it out with an air hose if possible. At the least clean it out as best as you can. This is a big problem on Ford engines and the ford dealer I use will warn you when you buy an egr valve.

Problem solved.
It was the PCV Valve hose on the R.H. side. The small rubber hose connecting the PCV to the rigid tubing that runs around behind the engine up to the Throttle body was melted, and was sucking in fresh air. The break was hidden by some foam insulation that "protects" the tube.

Also getting the readiness codes to clear was a problem. The EGR cleares right a way, but the EVAP and Catalytis system codes were harder. I finally got all the codes cleared today and had the emissions testing done. A pass.
I took a stop and go trip thru holiday shopper traffic up to the freeway then a 65 MPH trip of about 20 or so miles.
Thanks for all the help and advice.