Why does the engine light, brake light, oil light, cruise control light flash?

Hello, I do not think your transmission fluid being changed has anything to do with your warning lights. Diagnostic testing will reveal any active trouble codes for pursuit in troubleshooting. However, multiple warning lights also can indicate a power problem, such as with lower than needed voltage from the battery. Start by testing the battery and recheck from there.

What did your mechanic think was causing this concern you have? You did get your mechanic to take a look at this - right?