The way that short throw shifters work is that they are longer on the bottom ie. from that pivot ball down. This is so that you have to push/pull it less distance up top to move it further down below thus giving you shorter throws. So........sometimes they hit the heat shield that is blocking the cat. Any brand can have this problem the generic ones or the expenxive ones. You could get under the car and bend the heat shield just a little bit so that is won't hit.

Good luck