The TV cable setting is not that sensitive. However, the shift point at wot is learned by the computer. When you put a bigger TB on it, it is probably reving up faster than it used to and now it has the wrong learned shift point.
Explaination: the computer commands the truck to shift at wot by spiking the governor pressure several seconds before the desired rpm is reached. This causes the truck to shift. It knows that the truck has shifted by observing the sudden change in engine rpm. The computer knows that the tranny will take some time to shift. Before it learns the proper value, it will shift early so that the tranny has enough time to complete the shift without the engine revving too high. The computer will slowly command the shift later and later until it sneaks up on the correct rpm. This ensures that the tranny shifts at the correct engine rpm based on the amount of time your particular setup takes to shift, how fast the engine approaches the redline in each gear, etc.
If you are hitting the limiter before the shift, then the computer is commanding the shift just a tiny bit too late (based on its previous learned value). You need it to relearn the shift point, or have the rev limiter raised a bit in your tune. The computer will eventually learn the new point.
I would erase the learned shift points by taking the battery cable off for a couple of minutes or so.
