A poor running engine will create shifting issues in an automatic transmission. When cars come into the shop with a CEL lit after a visit to a quick lube, we often find the intake tract has been reassembled incorrectly by the oil change artist after he checks the air filter. If the JL uses a cheap scan tool, the findings are suspect. The scan tools at our shop cost thousands of dollars up front and require a similar expenditure every 4 to 6 months. Check to ensure that the "oil change artist" seated the air filter correctly after he checked it and didn't allow debris to get on you mass airflow sensor (or unseat it). If all is good, find an competent independent shop to scan your car. The average GM dealership does not seem to understand these cars.