HelloCustomer my name is Mike.
The most common cause for this is the ignition switch. The switch supplies power for all of the different electrical functions that happen when the key is on. There are several circuits in the switch so when they start to go bad only a few things will be noticed. The most common of these things to happen first is trans slippage and a check engine light. If you had the codes checked I would bet that you see quite a few codes. That also explains the ignition not shutting off. I will include replacement instructions for the switch. If you have more questions please ask.
Push down on the allen wrench to release the tab on the lock cylinder inside the lock cylinder housing.
Important: The gears between the ignition switch and the lock cylinder housing must be in the correct position. Failure to do so will cause a misalignment of the gears in the ignition switch and the lock cylinder housing, which may result in a NO START or BATTERY DRAIN.
Important: In order to reach a stop while rotating the lock cylinder housing gear you MUST push and hold in the solenoid on the electric park lock.