Missfire on 2000 Montana van

[ENDRO]

I have experience a random engine misfire on my vehicle. I puchased this vehicle several years ago with 70000 km. It currently has 90000km.
My non dealer mechanic suggested the dreadful tune-up to correct the problem. Guess what $500 later and the problem still existed. He suggest we replace a faulty engine coil, surprisingly enough, this did not work.
I decided to take the plunge and go to the dealer, with no warranty available the outcome will be nonething less than expensive. The dealer diagnosed the problem to be the injectors. However, the catch was that all 6 injectors will have to be replaced as not one was salvageable. Original GM injectors are $200 each so I had to go aftermarket. The aftermarket injectors were $70 each however it took 2 weeks to get the parts. The total cost was $1300 and add the $500 tune-up that is did not require and I at $1800. In addition lets not forget I was without a vehicle for over 2 weeks. My beef is that GM has service bulletins out indicating that a problem exists. The vehicle has had normal maintenance. The dealer had nothing to say except that the gas filter should have been changed every 35000 km. My confidence in G.M products has dropped and I'm looking to spend my hard earned money on an import now. Has anyone had this problem, and if so should I unload this vehicle given that these aftermarket parts are rebuilt injectors and G.M will only warranty the work for 1 year.