2002 Nissan Quest GLE - Shakes beyond 60MPH

I got it checked from an authorized mechanic workshop just before buying and they took almost 2 hours for checking each and everything but they only told me that there are 4 things -
1) One of the Engine Mount needs to be changed - though it is not must do at this time
2) Rear brake pad needs to be changed as they are at -5%
3) Transmission oil needs to be flushed
4) Time Belt needs to be changed

Can any one of the above cause this problem of Vibration. Pls advice.