I would try removing the EGR valve and cleaning the pintle area out before starting to replace parts. The EGR's tend to get clogged up with carbon and then start sticking. Also check the EGR valve for a ruptured diaphram. You can simply suck on the vacuum hose going to it and see if it will hold vacuum. Also check all of the vacuum lines going from the EGR to the engine, for a leak.

Good luck.