I block too. I've always had this kind of stutter and I feel like it's more painful than if you just repeat sounds. One thing I've noticed that helps - trust me on this - is to stutter on purpose. Instead of focusing so hard on getting the word "quarters" out perfectly, maybe try stuttering the first sound for a few repetitions, like q-q-q-quarters. Knowing that you're doing it on purpose makes that time pressure and anxiety just melt away, but you have to commit to it. It's called paradoxical intention - the same idea that says trying to fall asleep makes it impossible to sleep, but when you try to stay awake on purpose you get sleepy. It's terrifying to think that you're going to stutter on purpose and face the embarrassment and possibly ridicule - but wouldn't an easy stutter be better than a 20 second block? We can't be perfect, but we can have more control.