EGR Flow problems - 2001 Chevrolet Lumina

I am assuming that you vehicle is equipped with a 3.1L V-6 since you didn't mention it. (If this is not correct, please post a comment and let me know.)

You most likely have clogged-up EGR ports.
You will need an EGR-to-manifold gasket, a throttle-body base gasket, a wire coat hanger and a spray can of carb and choke cleaner.
EGR Valve gasket: FEL PRO part number 70804 - $5.99 at AutoZone
Throttle Body Base Gasket FEL PRO part number 61053 - $1.49

Remove the EGR valve and the throttle body. Cut the wire coat hanger so you have a piece about 8" long. Use the piece of wire to scrape and pick through the carbon buil-up in the port that goes between the EGR valve and the intake manifold. You can work from both ends by going at an angle through the hole in the manifold where the throttle body mounts and from the other side where the EGR valve mounts. Once you have broken through all the carbon, clean out as much as you can with the piece of wire.

NOTE: Try to not allow this stuff to go into the intake manifold area - engine valve damage can occur if this stuff gets stuck in a valve. It may be a good idea to stuff a rag in the intake just beyond the work area to catch the debris. - DON"T FORGET TO TAKE THE RAG BACK OUT BEFORE YOU RE-INSTALL THE THROTTLE BODY!

After most of the carbon is removed, spray the carb cleaner through the port to finish cleaning it out. After you are satisfied that it is as clean as it is going to get, reassemble the EGR and throttle body. Clear your fault codes and retest the vehicle.

This should do the trick.