Hi, I own a 99 Tahoe, 5.7L 4x4. I recently hit 150,000 miles and had to have my transmission rebuilt. When I picked it up from the shop I was paying specific attention to shifting. All was good, but the next day when driving to work I noticed a noise (ticking or air leaking sound). To me it sounds like an exhaust leak. Then my Service engine soon light came on. I don't know the specific code (believe it was P0430, but something Catalyst. I don't know if this is a coincidence or something the transmission shop did. They of course say it wasn't them, but I've been told they had to remove some parts around the transmission including the exhaust.