Chain Slips in certain gears I have noticed that I can not get my rear derailleur to sit perfectly allowing all of my gears to feel good. Mid range often feel a bit lumpy or there good when using either one of the front chain rings but not both.

I clean the chain once a week and I'm always fiddling with the cable tensioner screws, more than I think I should be. I recently replaced the gear cable.

The bike is less than a year old, its a nine speed Sora. 

Is it likely that I need a new chain already, the chain rings are a bit worn, not sure if too much and occasionally the chain seems to slip when i pull off (mid range gears) 



I just had the bike on a stand the back wheel is making a creaking noise when i spin it and the cassette has 5 to 10mm wobble, could this be causing the issues &amp; should there be that much wobble on the cassette ?

Also the Gear cable is frayed again - I only changed it 2 months ago.
I would guess that chain and/or cassette cogs are worn (typically middle ones go first) if you've tried adjusting and can't get it just right. I go through about a cassette a year on bikes I ride a lot, especially when I don't do a great job of cleaning and relubing the drivetrain. However, just replacing the chain can be bad if it's already jumping. It can get worse if you put on a new chain to the old cassette. 

You might be to the point where you need to clean your derailleur/ jockey wheels / front chainrings of any existing grit and replace both chain and cassette.

Other less likely considerations could be:
 - A damaged freehub body (if you have an aluminium freehub body).
 - Misaligned Derailleur hanger (as Nathan Knutson Mentioned)
 - Poorly Adjusted or damaged shifting cables, or cables that are corroded / sticking in cable housing.