2012 Hyundai Elantra Limited Used Car issues

So I got this car a couple months ago from Carmax, cosmetically its perfect
but I notice such awkward things. First thing I've noticed, it idle shakes, like
a manual would before it stalls out. I took it back to carmax and they said it
was "within range" and i just got over it, usually it doesnt shake or shake as
bad when i turn the ac on. Next, I noticed that when I'm driving it kickbacks
two or three times then keeps going. I hate it and even when I'm not in
drive, I'll have the ac on to calm the shaking and i still feel it 'jump' back and
every time the ac while slow down and then start back up when each
kickback stops. The most worrying bit was yesterday. I was making a left on
a road where everyone is in a rush to cut people off and I pressed on the
gas a little more than usual to quickly get going and i had my music up and
i heard this awkward horrible revving sound and noticed it was my car. I felt
it and it sounded .. strained?  I immediately took my foot off the pedal and it
slowed down but the rpm gauge was bouncing back and forth from 6 and 7
even though it was slowing down to 25mph. I coasted to the side of the
road and i turned the car off, gave it a minute and then started it back up
and it was fine. Its been fine today too, but jesus if i knew it would be this
worrying i would have just gotten a new car. Also the screen almost always
has a pop up of an app failure, will freeze, today it didnt show me my back
camera , and yesterday it wouldnt connect to bluetooth. Im constantly
having to restart the screen with a pin.
Someone help please.