How to make something look large

Hey, this is even more fun than working on my own pictures.  

As near as I can recall, this is what I did:

Lightened overall.  'Stretched' the sky at the top with warp tool to remove some of the clouds.  Used color selection tool to select just the foreground - and then used the levels tool to darken the blacks and lighten the mid-tones there.  This has the side-effect of increasing saturation.  I left the background alone to keep that misty-far-away look.  I did saturate the sky just a little though. Added some light to the mid-left slope.  Too much?

Looking at it now, I wonder if you wanted those top clouds for a stormy look?

If you wanted to 'stretch' the scene, but leave the vehicle alone, you could add some canvas size at the top, then use the rectangle marquee tool to select all but the vehicle, then edit>transform>scale and pull the top 'handle' up.

Best not to overdo the 'stretching' thing.  Like many Photoshop adjustments, it's easy to go too far.  Think 'subtle'.