[quote=hyarnell1]
EGR valve seems free (diaphragm moves freely)
QUOTE]
At this point the valve itself seems suspect. I'd do all the inspections and adjustments that Maxwedge suggests, particularly the timing. I'd then pull the EGR valve itself and inspect the pintle. While it's off, inspect the passages at that end for carbon deposits. In your place, and if the passages at the EGR end aren't too bad, I'd just replace the EGR at that time because it is such a PITA to remove and reinstall. Don't forget a new gasket. The old one is likely to come apart.
FWIW
YMMV