So, I just had a new tranny installed today (4L60E) on my 01' SS. My old one was baddly slipping and finally, the flexplate blew on me. The new tranny is in place, but it seems to be slipping still, but not the same way. The tranny feels strong, but under moderate to heavy acceleration, it will slip, and kind of studder. Under regular acceleration, it seems crisp and just fine. It also seems to have loss some power under mod/heavy acceleration. Does this sound like something the CAT could be causing? The car has 90,000 miles on it and is all stock. I've heard that a bad CAT could give a false impression of a bad transmission, is this true? I know that the tranny and torque converter a brand new.

 

Check and make sure there's nothing rattling inside your exhaust system. Might be broken pieces of the cat. Might be the perfect time to buy a magnaflow hi-flo to replace it, or even better yet LT's and a new dual cat y pipe.