That's completely normal behaviour for a locked TC. If you release the pedal, the TC unlocks so it doesn't get subjected to engine braking forces. Similarly, if you increase the TPS voltage by pushing the pedal without the road speed rising, it will cut out the lockup.

As mentioned in my previous post, it's easy to test with a voltmeter. You should have 0.4v to 0.6v at closed throttle gradually (do it slowly so you can see any sudden drop on the voltmeter) rising to ~4.5v.