I got this car semi recently as it was in decent condition and $500, when I have to give it more throttle to pull out into traffic and the vehicle gets more than 3000 rpm and it shifts the car squeals and one large shake as it's shifting, I took it to a shop and they told me it was the transmission mount as the rubber had deteriorated but even after replacement it doesn't do it as bad but it's still there. Is it time for a new transmission?

My car runs and drives but it makes a squealing noise and will shut off occasionally