Need Information about Dashboard Lights

[PKK]

B14 GA16DE

My Check engine came on with P440 P446 error, so I took it to the Dealer to fix. they changed my Evaporation Pressure Sensor, reset the light and asked me to come back after couple of days to obtain the Inspection stickers. They also did Oil service.
Unfortunately, at the end of that week again the check engine light came on. Through Auto Zone, I found the error code is P770. Auto Zone people suggested me to check the transmission oil level first, so I checked and add one quart right away; Besides, they said that the light will go off in two days. Still the light is on.
One more thing I worrying about is, while I am driving, "Brake" and "Battery" dashboard lights are often flickering, and check engine light is permanently on.
I drive 30 miles one way to my job every day. I am hesitant to go to the dealer because they charge too much. I am wondering how the dealer missed to check transmission oil level when they did oil service two weeks back.
Can anyone has any idea about "driving with flickering "Brake" and "Battery" lights are safe? I am supposed to get the Vehicle Inspection stickers as soon as possible.
Please I welcome all suggestions.

Thanks
PKK