MacBook Pro External Monitor Resolution
You can try Display Maestro :


  Unlock all display resolutions Display Maestro gives you full control
  over attached displays, allowing the usage of all available
  resolutions and bit depths. This is done by ignoring the operating
  system setting of hiding potentially unsafe resolutions.
  
  Restore legacy depth modes It is ideal for running legacy games which
  require 256-color mode and do not automatically switch the screen
  depth for you. Mac OS X 10.5 Leopard removed the ability to set 256
  color mode manually using the built-in preferences pane, but the
  feature is now available here in Display Maestro!
  
  Light-weight and background-friendly Display Maestro is a small
  application which can be configured to launch during login, and sits
  quietly in the menu bar. Upon exit, it will also automatically revert
  your display back to the resolution chosen before it was launched.