Well, the learning continues.
I have discovered that manufacturers put the cable routing groove in deraillerus for a reason, and it IS possible
to miss that groove when installing the cable if you are not careful.
This may result in poor shifting in the rear.
I discovered that I had indeed missed the groove when installing the shift cable after going through the usual
suspects (new cable and lubing all sections of housing) with no appreciable improvement.
Still would shift up, but not down, or vice versa (a tired topic 4 sure.)
This started after exchanging a new 10 speed 105 RD to replace a 9 speed of the same, and
realizing a degraded shift.

Oh,well, should be better now.............

It's also possible to misroute a front derailleur cable by passing it under, not over, the little tap beside the clamp bolt. All sorts of poor shifting have been fixed by routing it correctly.

Been there,done that,too!