Well, I found myself under the truck today so I did some looking.
With the KD linkage all the way back at the carb, the lever at the transmission still has 1/2"+ of travel left in it. I can PUSH HARD on it at the carb and take up most of that last 1/2".
I'm guessing that last half inch is where full throttle kickdown would be engaged?
Moving the lever at the transmission against the stops felt pretty firm, so I don't think it's broken inside.
The linkage itself has some slop in it, so I'm sure that doesn't help any
Probably time to start looking at cable prices.
-Dave