I think I might have found the culprit. After ruling out lever differences, I decided to take a closer look at the cable to see if it was unwound or if one of the ends had worn down. I wiped down the end and the towel caught on something near the end of the cable. Upon closer inspection, it looks like the cable has been rubbing against the sheathing and slowly wearing itself down. Now to order another one and cross my fingers. This is an expensive hobby. Not as bad as golf but close.