2006 Ford Freestar need your help

Ok, so about a month ago our van started bucking at about 45 miles per hour, with the sputtering during acceleration. This was more pronounced when the a/c was on. Eventually the check engine light came on. The code was P0301. A buddy and I replaced the plugs and wires. About 15 miles later, the light came back on and the same symptoms reappeared. I had my wife get a code run on it, which produced P0300 (misfire in cal. 1). Went back and replaced the ignition pack. After driving it for a while and noticed the absence of sputtering and bucking, along with smooth acceleration, I smelled victory. Then, the next day the check engine light reappeared. I had my wife get a code run on it and it came back P0401. I cleaned out the erg valve (it wasn't that dirty either) and put it back on. Although it drove nicely the light came back on. I got another code and it came up P0401 and P2006. Not sure where to go with this. Any help would be greatly appreciated.
Thanks,
Scott