My 72 GS455 four speed developed a bad hesitation when you floor the gas pedal, this has been a problem for quite awhile. I have had several people make guesses as to what the cause is however no one could really pinpoint it until I called Ken and described my problem. He told me it was most likely that my secondary vacuum pull off was pulling the secondary air flaps open too quickly causing the hesitation. He sent me a new vacuum pull off along with the vacuum line that he put a restricter inside, he told me that if this didn’t work then also tighten up the spring on my air flaps. Ken shipped it the same day and I just installed it and my hesitation is completely gone, my car is back to tearing up the tires. And all for $13!!!! Thanks Ken and Eveveryday Performance