1996 Sable - Insufficient EGR Flow

I have a 1996 Sable that I am getting the P0401 code, insufficient EGR flow. I have replace the EGR valve, EGR solenoid, and the DPRE switch and still the same code. Any suggestions?

Have you reset the computer? An easy way to reset it is to unplug the positive battery terminal for about 30-40 seconds, then plug it back in.

Yep I did, and unfortunately after about 50 miles of driving, the darn thing comes back on.