[Closed] Rear derailleur adjustment

Either the cable is too tight, or, more likely if everything else looks o.k, the cable is sticky and needs cleaned and lubed, or replaced.

Sounds like it could be cable stiction in the gear housing or perhaps a small kink in the cable - the return spring tension of derailleurs is very slight and it doesn't take much to cause problems, pop your gear cable housing out of the stops, change up to the top of the cassette then without turning the cranks tap the shifter all the way back down to the 11/12tooth, the cable and housing should be slack enough to pop it free from the cable stops and spray the cabe and housing liberally with gt85/wd40 or similar as you work the outers up and down the cable.

Is the shifting from smallest to biggest cog not affected by overtight cable? Played the barrel adjuster 1/4 click at a time to loosen it to no avail

sounds like you need to start again as the cable tension is not right.
undo the gear cable, make sure the shifter is in the highest gear (8,9 or 10 depending on what set up you're running) and the chain is on the smallest cog.
once you've done this make sure any barrel adjusters on the rear mech and shifter are completely wound in.
now all you need to do is pull the cable until the rear mech aligns itself under the smallest cog and then tighten the bolt to secure the gear cable.
once you've done this your gears should shift smoothly up and down the cassetts. if it the chain does not shift up make small adjustments on the barrel adjusters to place more tension on the cable, but be careful as too much tension will result in the chain not shifting down.
but to be honest you wont have to do this for a while as its something you do to compensate for cable stretch...
i do take it you are using a new cable....if you're not now would be the best time to do it....it'll improve shifting performance

Its an slx 10speed, still the stock cable when bike bought last april 2012.. Its a bit dodgy on its shifting last couple of rides.. And kinda got time today to sort it out.. You not gonna suggest i definitely need a new cable right ? 🙄

And outer probably!! Wet weather kills cables, and this has been the worst year for a long time!!

its not going to help you now but it's worth keeping a roll of outer and some inners to hand. I usually just replace the cables if the shifting is getting dodgy and that usually solves the problem.

you might just get away with cleaning and lubing though if you are keen to get out and ride

Thanks guys, and to @nosedive who answer the doublepost. Will try to get new cable and outers if it can sort the problem.. If not.. Well the worst that could happen is i have two perfectly good cables 😉