Please note that since you are on shared hosting, we are forced to restart MySQL as soon as there is a threat for the server's stability. However, we do not restart it very often.
Also, as a shared server customer, you will not be able to edit the values for key_buffer_size, read_buffer_size, etc.
All this will be possible for you on a dedicated server.
Also, please let us know why you chose to set your cookies time setting to 3000? Was this a recommendation of vbulletin support?