M-10: rear end: 
http://www.flamesofwar.com/Portals/0/all_images/american/Boxes/UBX31c.jpg
M-18 rear end: 
http://svsm.org/albums/M18/IMGP0928.jpg
M-10: rear end:
http://www.flamesofwar.com/Portals/0/all_images/american/Boxes/UBX31c.jpg
M-18 rear end:
http://svsm.org/albums/M18/IMGP0928.jpg
Yeah, I looked at the sloped sides and the low profile turret characteristic of the tank destroyers, then jumped to the conclusion it was the M-10 without stopping to look at the wheel train. Then the browser crashed the computer, so I had to reboot and take another look at the tank destroyers, counted wheels, matched the wheels to the M-18, jumped over to FR...only to find you sly guys beat me to it. :)