2000 Saturn EGR problems

A while ago my Service Engine Soon light came on. A mechanic told me it was a faulty EGR. Since the weather’s been warmer lately, I have experienced significant loss of power on the highway especially. Instead of paying over $300 to have my mechanic fix it, I bought the part and went to replace it myself. I ordered the part from Checker (possibly my first mistake?) and they sent me a Niehoff valve. When I put it on, the Service Engine Soon light went off right away, and the engine idled magnificently. As soon as I went to drive it, however, it was a different story. When I step on the gas, the engine jerks and stutters, and the power is completely gone. I can floor the gas pedal and then everyting kicks back into gear and I can drive, but I have to either constantly have the car at idle, or floored.

So I returned the valve, thinking that it may be a faulty valve. The auto part store would only replace it with the same part, so I got the new one in and put it on today. Same problem.

Does Niehoff make crappy parts? Is there some incompatibility between Niehoff parts and Saturn vehicles? Any ideas?