Chevrolet Repair: 2003 chev express van 6.0 liter, fuel situation, oxygen sensor

Question
I'm on vacation 1000 miles from home.  Engine check light went on a few days ago with periodic rough idle.  Today engine check light started flashing and vehicle would hardly run.  I had it scanned ($90.00) and they said only every other cylinder was firing and that I need a tune up which they scheduled for tomorrow AM.  After leaving that repair shop, engine check light went out and the van has run smoothly all day.  What should I do?

Answer
For every other cylinder to be firing and the other ones to not, it sounds like a catalytic converter.  There have been alot of Cats going bad, which I think has to do with the fuel situation.  most companys are getting the cheaper fuel to sell to the public, because of the rising costs.  I really don't think a tune up will help every other cylinder.  It may just be a fuel deposit stuck in one of the fuel rails, but a tune up is not going to help that.  From the info you gave me it truly sounds like a bad catalytic converter or oxygen sensor.  Especially if its running okay now.
Jimmy