Why is my transmission light on and can I fix it?

Hello, this is more than one concern likely -- the transmission light is one thing, but the engine performance is another. Diagnostic testing must be performed; the presence of warning lights shows that there will be diagnostic trouble codes stored in the memory of the engine's computer - so that will be helpful to provide clues to troubleshoot what is happening. The engine performance and preventing going over 20 mph may be the vehicle's processors preventing further damage from occurring. Get some professional assistance before attempting to drive further.