2003 GMC Safari

Engine Performance problem
2003 GMC Safari 6 cyl All Wheel Drive Automatic 73,550 miles

I only drive back and forth to work, which is minimal driving but some highway.
2 months ago the ignition coil came loose and I paid to have it properly renstalled.
Last month the " check engine light" came on and I had the oil changed.
They notice immediatly that the gas cap was not on correctly and that a P0442 error was present.
Several weeks ago I notice the engine hesitating and pulling when I reached 50+ MPH. It was not consistent and would only happen intermittently. A week later it was noticeable after 40+ MPH. Also not consistently. Then it was at any speed but again not consistent. I purchased gas at questionable gas station and thought I might have bad fuel. So I put High Octane [94] in the next fillup. This did not correct the issue.
Today as I pulled out, when the excellarator was pushed it pulled very hard over and over again until I eased up and allowed it to switch gears and it never went more then 25 MPH's. I went to a local parts place and ran their scanner and received the following codes: P0101, P0420, P0756, P0300, P0404.
I am not sure what to do now and it all looks expensive to me.
June 22, 2010.

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