The car sometimes bucks like the engine rocks was told by local shop to replace the rear motor mount to fix this problem does that seem right, cause the tranny seems to shift fine, anyone had any problems with this its my girlfriends car?

 

most likely mount.. had that prob before

 

Well does it buck between shifts or does it do it randomly while driving?

If it feels like the engine is rocking between shifts than I saw look at the mounts and see if they are falling apart.

If it is doing it at random then you might have a worse problem than mounts.