New tacoma owner 1 issue with a vibration

Hello, I hope everyone is having a good day. So I bought a used 06 Tacoma PreRunner double cab long bed and iv'e noticed that while driving at 25-30MPH I feel a Vibration then goes away. I took it to the dealership and was told the tires needed to be aligned/balanced for the vibration to go away... I paid for the service (unfortunately the warranty has expired) and guess what? The vibration is still there.I took it back to the dealership and after checking everything, they said I needed a new transmission. The previous owner did get the transmission rebuilt at 125k miles now it has 191k miles. The truck runs very smooth...but that vibration is getting to me. My tacoma is completely stock. I am here for help and advice in getting this issue fixed. Thank you everyone!