Rear gear change misses 1 gear Hi I have a 9 speed setup with the derailleur that springs to the largest cog.

My problem is that when I change through the gears one at time it misses 1 whole gear in the middle. It doesn't sit and "chatter" trying to change, it just jumps over 1. When I get to the smallest I still have one more shift on the shifter.

I am reasonably experienced at getting gears indexed and can normally get them right but this is driving me mad. the low screw is set just right and their is no slack on the cable when in the low gear. It changes fine the first 2/3 gears then misses one and carries on fine to the highest the same in reverse.
any ideas?

Thanks
Hard to say exactly what is going on but I suspect the problem is in the cables and housing - either a routing problem or the cable is sticking.

Inspect the cable run and ensure there are no kinks and the housing is inserted in frame bosses properly.

Pull the cable out and clean it, lubricate and re-install (can be hard of the tip of the cable is frayed). Even better, replace cable and housing which is relatively inexpensive.

Re-adjust the derailleur. Start by rechecking the high and low limits. Start the indexing on the smallest sprocket - that way you know you won't have the problem of the derailleur arriving on the smallest sprocket with on click to go.