You need to get to the bottom of that, because the KD mechanism pulls double-duty by increasing the line pressure as the throttle is opened, to prevent clutch/band slippage.
It is possible for the internal lever to drop down under the pressure valve, and then it does nothing, and soon your trans pays the price.
Disconnect the lever from whatever controls it, and then push it towards the rear of the car. If you feel spring pressure, and the lever returns to rest, about half-way to the front, then it's practically guaranteed that the parts are in the correct orientation.
If you can't get the KD to work correctly, then Zip-tie it all the way to the back, until you figure it out. This tie-back should delay the upshifts considerably, and make them more harsh. If you can't stand it, put a lil slack in the Zip-tie but don't floor it any more, maybe disconnect the Secondaries.
Then figure out what's wrong with your shift cable.
Be advised that if you have changed the rear-end ratio, to something more sporty, your automatic-shifts may occur too early. If this happens to you, the proper solution is to install a lighter flyweight in the governor. Fine tuning is with springs. The governor is in the tail. Dialing it in is well worth the trouble of doing it.