[Racer-X-]

Are you also using a vacuum switch with that? Thats usually the way I've set them up. So the TCC unlocks when vacuum drops (when you stomp on the loud pedal).

 

[Racer-X-]

I had not planned too. Im just using a switch on the dash to turn it off when not needed/wanted. Just keeping it simple for now.

Either tie a string from the switch to the accelerator pedal so when you floor it, it turns of the lockup, or look into Superior K058 vacuum switch and run the lockup signal through that in series with your pressure switch on the 4th gear hydraulics.

The converter clutch will let go if you unleash full power from a V8 on it. The only question is whether it's going to slip and wear out/destroy the clutch material very quickly, or whether you cut power to the TCC solenoid and deliberately disengage it.