I've had my car for 2 mnths

I've had my car for 2 mnths. Now. But 12 days after I bought it, it srarted messing up on me. Here's what it's doing. You can be driving along and all of a sudden you'll fill like something shifts in the trans, It will stay stuck in 1st gear till you pull off the road and cut the motor off, in park, start it back up and it's fine for a little while longer. Does it mostly when it's hot! Been in shop twice now, they can't find anything wrong! Had diagnostic run and 25 bad codes came back on it! I am out of options! Just found out the motor was replaced before my purchase!