When I shft from the 3rd gear to either 4 or 5 it will not shift, I have to shift up to the 6th gear and then down. Before I start messing with this, my question is this: Would this probem be due to a cable that needs adjusting or is it the deraileur itself that is suspect. The bike only has approx 1500 miles on it and had a complete tuneup at about the 1000 mile mark at the LBS.
The first thing you should do is eliminate the shifters. You didn't say if it was Shimano or Campy, but in either case make sure the shifter is well lubricated (a spray lube with one of those long nose tubes will work great). Then make sure all the cable housings sit properly in their places with no kinks..
If this doesn't solve the problem, try to adjust the derailleur. But make sure you follow directions. Either Shimano or Campy website have a PDF with direction. Or take a look at the Park Tools website for a more general procedure..
If not of those work you may have a bent derailleur or bent hanger..
The first thing that I would check would be the derailleur hanger alignment. I doubt your problem is in either the shifters or the derailleur.
Thanks for the reply.....the derailleur somehow was bent about 1/4 inch. I am not sure where this happened, I have not had any falls or accidents. Anyways the problem is fixed after a few minutes with some pliers and readjustments.