Jerky over-run

Having solved my sticking throttle problem with help from this forum, I seem to have created a new fault. When slowing down in first or second gear the car becomes very jerky. I guess that when the throttle was hanging up it kept some power on working against the brakes and this has been eliminated. Therefore I'm guessing that the rear engine mounting is failing and the engine is rocking back and forth with the torque.

Is this right? And if it is, do I have to get all three engine mounts changed or can I get away with one? I'm thinking this is beyond my skill or at least my equipment so it will be a garage job I guess. Has anyone had this done and got an idea how many hours I would be charged?

Thanks again

Michael L