I have a '95 Lumina sedan with a 3.1L V6. At high speeds the Check Engine light will often come on. Scan reveals EGR misfire - cylinder #2. I replaced the EGR valve (with a used one), cleaned out the carbon build up in the manifold, and replaced the gasket. Light continues to come on with the same code. What should I do next? Someone suggested checking the EGR modulator. Any suggestions?