Check your engine mounts (Holden Parts they are called Dampners). When the mounts crack and sag, the engine sump will contact the k frame and make the car feel really rough.
Easy to see, if you can fit your head underneath the engine, at the back of the sump you should nearly be able to fit your little pinky finger between it and the k frame. There will also be evidence of marks left on your sump.
Ken.