Originally Posted by masi61

I would replace that cable with a non-polymer coated. The stripping off coating will hang up inside the housing. I use the Jagwire burnished stainless inner wires.

Originally Posted by dsbrantjr

Or shreds of that (IMO bad idea) polymer coating jamming things up. .

Originally Posted by Crankycrank

As mentioned that shedding polymer can gunk up your shifter. At least push the head of the cable out from the shifter for 1 1/2" and scrape off the polymer coating. Better yet just replace the cable as it is getting in the risky zone mileage wise. Also another vote for checking the hanger alignment since the OP mentioned troubles started after the derailleur got bumped and before replacing chain and cassette.

Originally Posted by dsbrantjr

If you decide to replace your inner wire, just use die-drawn stainless, it has virtually the same coefficient of friction against the PTFE housing liner as the coated stuff, doesn't shed and is easier to clamp securely.

Originally Posted by Iride01

Assuming the 5 - 6 k is 5000 to 6000 miles and not 5 - 6 kilometers <grin>, then check that the cable isn't frayed up in the shifter. Especially if these are STI's, I don't know if it's an issue for other shifters. My son's Tiagra 4700 had indexing issue when going from the bigger cogs to the smaller cogs and his cable was frayed in the shifter after only 4000 miles.