I am having the same issue with my 3.4 2005 ls, and called the dealer in town to see if they could check out my catalytic converter. They said there is no way that they know of to check out the cat. I thought someone on here said that there was some sort of pressure test they could do to check it out. I have 90,000 miles on the car. Could the catalytic converter be causing the hard shift? And if so, what tests have you guys used to check out the cat? Or do I just throw on a new high flow cat and pray?