Overflow Box Too Small?

[muck]

Seems to me the bulkheads can handle that amount of flow but your overflow boxes can not. What are you overflows rated for? Should say on the box I would think..

Is drilling the tank an option? Thats what I would do if I were you.
If not you have two options.

1. Get a smaller GPH rated pump that the overflows will be able to handle.
2. Return the overflows and get larger ones or DIY larger ones.