Transmission With No Gears?
 

Hello y'all. First time posting because I'm really confused as to what happened to my truck today. About a week ago I bought a 2012 Chevy Silverado with a 5.3 and 128k miles on it. It has been a great truck up until today where I was driving normally and I pressed the gas pedal to speed up after a light and I don't know if it was my fault or what but the truck suddenly jumped into overdrive and made the transmission hard shift. As in I heard a clunking sound and it was a pretty bad shift. Now since I wasn't expecting it as it had never gone into overdrive with such little pressure on the pedal, I instinctively pressed the brakes to slow down and I think it made a hard shift down. I continue driving and that's when I noticed that it felt different to drive. It wasn't shifting anymore. Or at least it didn't feel like it was and yet the truck drove normally as if it were shifting. Then I noticed the rpms would stay at a high level while going low speeds. I was going 35mph to 40mph and the rpm would stay at around 3000 while I was just trying to maintain speed. Also it now speeds up very quickly by pressing the pedal only a little bit. I don't know what happened and I'm worried I broke my transmission. What do y'all think?