Instead of paying for a brand new transmission, I had the dealership install a used one. After I've driven around 50 miles, it takes 50k rpm to shift up. The gears don't slip, but it hard down shifts. I need your expert advice in what to do.
It sounds like the transmission is mechanically sound if you are experiencing no slippage. You will want to have the transmission fault codes read out to see if there are any issues that could be inhibiting the shifts. Other possibilities could be a faulty valve body or faulty solenoid. Once again knowing what faults are stored could help with the diagnosis. You may want to enlist the help of a mechanic or transmission service center, who will have the equipment and expertise to inspect why you are unable to change gears properly.