Use a mill file to radius the top edges of the cable groove in the quadrant, 1/16" or so. Years of experience made me just do this automatically when I installed my UPR quadrant--that was 4 years ago with the the original cable, it's still looking fine 70k miles later.
Also make sure the quadrant is aligned with the adjuster--you said you did this above, but double check it and get the spacers right. Stick a piece of coat hanger or stiff wire through the front of the adjuster and have it lay in the groove of the quadrant; make sure it come straight out of the firewall.
In the last apply some heavy grease to the cable and quadrant groove--doesn't have to be "slathered" but a goodly amount will help.