I have found that decreasing the amount of time I spend on cardio will help me break through a plateau. The secret is to work out at a higher intensity. If you normally work out for 30 to 45 mins at a moderate pace, try working out for 20 to 35 mins at a faster pace or at a higher resistance.
Sometimes hitting a plateau means you need to rest. Don't spend so much time at the gym for a week and see how it goes.