'97 Ford F-150 misfires on 3 cylinders

I have a '97 Ford F-150, 4.6l V-8, automatic, with 180,000 miles. My truck ran fine, until a week ago. I filled the tank with gas and drove about a mile and it started lurching and shaking and chugging. I though I had got some bad fuel. I dumped in some Justice Bros. Injector Cleaner, and continued driving. It never got any better. I stopped at a service station, and had it diagnosed. The codes came back as the EGR vavle was open, and misfire on 2, 3, &7 cylinders. The check engine light has been on for a long time. And now it is flashing. (I had it to my local Ford Dealer, a year ago. And it cost me $800 to get the check engine light off. They replaced one spark plug and one wire, and cleaned the carbon out of the EGR Port, The whole while I never noticed any misfire problems until now.) The check engine light stayed off for about 1 week. Back to the facts, I changed the fuel filter, and checked the fuel pressure, 32psi, and 40psi with the vacuum line off the regulator. No change in the problem. I installed new plugs and wires. Gapped the plugs at.062". Still no change. Listened to the injectors with a stethoscope, and all seem to be cycling. Pulled the injectors and cleaned them, still no change. Pulled the #2 plug and it was black and wet. Put it in the plug wire and grounded to the block and it sparked as it should. I haven't checked to see if the ground strap from motor to frame is not making contact. Don't know if that could have any effect but I have run out of ideas. Anyone have any clues? I have run 1 and 1/2 tanks of gas with no results. I also made sure I didn't have any crossed plug wires. And it backfires at about 30mph if you step on it.