Trouble with team fortress 2

[vass]

I am having a hard time getting team fortress 2 to display at 3840 x1024.
I have seen someone post screens of the game running at that resolution, but have not been able to get that resolution.
I am using triple head 2 go and have not had this issue with any other game in recent memory.

If anyone could tell me what I am doing wrong, or offer any help at all that would be great.

Thanks