You need to get another mechanic.
Best bet is to take it to your Chevrolet dealer and have them fix it.
Sounds like the fuel injection. A problem perhaps?
There is no such thing as a low Tranny fluid light.
You have a dipstick for that as well as the oil. Seems you got ripped off. Only light that comes on in the Communication Center is your Change oil Light.
Have the dealer run the codes as sometimes there is a problem that will NOT turn on the check engine light. A code may be present. Thats about 80 bucks in some dealers.
A shame that shops and crooked mechanics can do that to you.
Lets find out the problem!
John