1997 Chevy Lumina EGR Valve

First code was miss in cyl. Five. Since wires had over 100,000 miles on them, I replaced them. Reset comp. Then I got code for heater malfunction on o2 sensor after conv. Replaced sensor & cleared light. Third time it was code 401, low recirc exh. Gas. Replaced EGR, drove car around for about 25 milesor so. Light hasn't gone off. Do I need more driving time or is there another problem. Since there is 152'000 miles on car, I just figured those parts needed replaced.I have two cards with money left on them with $8.30 on them.I don't use cards on the internet.I appreciate any help I can get.I'm out of work & need to pass emmisions test. Thank you for your time.