I didn’t know that the text was embedded in the image. I thought that the text was in a separate layer inside the Revolution Slider. Revolution Slider will try to maintain some minimum height of the slide sacrificing the width and will try to accommodate the captions(text) within the specified grid (in this case 1140 grid). Since you have the text embedded in the image, slider will just treat it as a image and not as a separate text layer.
Try re-sizing the slider in our demo site and you can see the background images are getting cropped while the text is being moved to the center because we have put the text to a separate layer.
Here I am going to suggest few solutions that might help.
1. If you want to keep the images as it is and still get a better result, then use the grid width as 1920px. That way Revolution slider will not sacrifice the width, but as the devices get smaller your slider height will be small.
2. You can use Flex or Nivo Slider that comes with the theme and they will do a good job of not cropping the image
3. The best would be to recreate images with the text within the 1140px width and not beyond that. See the screenshot attached, where it is clear that the text you have in the images go beyond the 1140px content area. You will have to move the text to the middle as we have done in our demo site. Revolution Slider will assume that anything beyond the grid width is not important and will try crop it when necessary.
Hope that helps. Thanks!