1996 Chevy Lumina Will not start.

I have a 1996 Chevy Lumina LS. I got it from my sister she was the only owner. It had a miss so she took it to a Chevy dealer and their scan showed DTC Po401 stored, EGR failure due to intake blockage. They then replaced EGR valve cleared intake ports, cleared DTC. That was on 7/8/2010. It ran great for 15 miles. She stopped at the mail box and it hickup and then started running rough again. My brother in-law replaced the front 3 plugs with no gap plugs but couldn't do the back three. It still was missing out. When I got the car I drove it and within 15 minutes it did have a miss. I ran a scan and if came up with p0301 (misfire # 1 cylinder). I install the same type plugs in the back. It would start then die. So I changed all the plugs with gap type at 60 thousands and wires. I checked to make sure it was all correct 5 times. Now it wont start. I checked for spark and there is blue spark. I checked the fuel pressure by removing the cap and pushed the valve and it blew right out. I cleared the codes and and now it shows 0 codes but still wont start. By the way the EGR valve was also replaced 11/11/2008 by the same Dealer. This is a 1996 Chevy Lumina LS.