P06A3 and P0300/P0303 codes; transmission won't shift

Hello everyone,

My 2011 Chevrolet Aveo LT has been fantastic for me for the past five years I've had her with minor issues here and there. Recently, the car was having an issue with it being in park but the RPM's still fluxing between 0 and around 1.5. I got the spark plugs changed out which was a good thing regardless because they looked pretty rough, and there was a tube that had a huge crack in it that got replaced as well. When starting the car back up, it would shake rough and then idle out. If you gassed it and kept the RPM's above 3 for a minute or two, it would last longer, but eventually idle out again which wasn't an issue prior.

So, spark plugs and tube replaced, the issue was still there but now with idling.. It seemed there was an issue with the throttle box/sensor as told by the first car reading (unfortunately don't have what code they give as I didn't bring it in). Once the throttle box came in yesterday and was put in, the Aveo started shaking very bad when starting up, but it didn't idle out (RPM's now stuck at around 1 rpm in park). The car was drove around and it couldn't shift past 2nd gear at all, stopping speed at around 25 MPH. I took it to O'Reilly's for a reading and I got P06A3 for "5V reference 4 circuit" and P0300/P0303 for misfire of the third cylinder (I say both of the codes because the specific P0303 showed, then he cleared the codes and P0300 showed up).

I am not the most mechanically inclined, but I would love for my car to be back in shape. If I could please receive any help or if anyone needs more clarification on anything, I will be ecstatic to hear back from someone. So far from reading forums, it seems it could be an electrical issue and maybe a coil pack replacement could work, but I wanted to reach out first as I've already spent a couple hundred and don't want that number to get ridiculous for no reason. Thank you for your time, and happy driving!