You are doing it wrong! Bring back the original settings!
You just had to change add_image_size( 'slider', 1018, 460, true ); this one. And had to increase the size for height instead of width. something like this would do add_image_size( 'slider', 1018, 660, true );
The re sizing works, and it actually did fill out correctly after changing to 700 instead of 660. However now one of the pictures is a different size than the others.