Joined: Jul 2015
Posts: 7,331
Likes: 3,199
From: NW Oregon
Bikes: 1982 Trek 930R Custom, '91 Diamondback Ascent w/ XT, XTR updates, Fuji Team Pro CF road flyer, Specialized Sirrus Gravel Convert, '09 Comencal Meta 5.5 XC, '02 Marin MBX500, '84 Gitane Criterium bike
the symptoms you described are because of a too-tight cable adjustment.
loosen the cable's adjustment by turning the adjuster in one click to reduce the "reluctance to shift to a smaller cog" in the rear.
it may take two clicks.