Do you have bare cable running along the down tube? Hold on to the RD cable lightly while you shift through the gears. If it get quite a bit of slack in it as it does those mis-shifts, then you probably have issues between your fingers and the RD. If the tension on the cable seems fairly constant as you get those mis-shifts, then you probably have issues between your fingers and the shifter.

Gummed up DR, shifter or cable can be the culprits as well as frayed cable inside the shifter or even the cable housings. Too tight a bend or maybe something you recently clamped over the cable housings might be especially suspect.

Does the RD move freely when the chain and cable are removed from it?