Servo shot. Rebuild the trans.
That's it? No other solution?
If it is, in fact, a servo, that part needs to be replaced, not necessarily
the entire transmission. OTOH, once it is out of the car and apart, the
labor portion is pretty much the same no matter how many parts are replaced.
If you decide to take the car to a transmission shop, try to get
recommendations first. Some are reputable, others are less so.