What might this be?
 

I'm not sure this is the right place to post this but having issues with our van and need some insight into what it likely is and how much it will cost to fix, before taking it to a mechanic. I'm fairly certain it will be VERY pricey and need to decide what to do about it....

It's a 2013 cheysler town and country and when going above 50mph (roughly) it struggles to shift into the highest gear. Not always, maybe 50/50. The times it is going to do this it also has a hard (slow) time accelerating even in lower gears. Today while driving it was having a hard time accelerating and then suddenly took off and then wouldn't stop. Kept going faster and faster as I tried to stop until I put it into neutral (it was still revving) and then turned it off. It then wouldn't turn on. Then the brake pedal clunked and it was able to turn on and drive normally.

I know very minimal about vehicles but I know this probably isn't good 😬

The fact the vehicle still moves under its own power is a good sign. Since your story ‘turned silly’ and you gave us no maintenance info , I think we should stop right here, stop driving the vehicle and locate a reputable MOPAR tech.