1) if you have regular color wood, you can change color mode to convert to gray.. another nice bonus of this technique is that it will reduce the filesize by roughly 1/3 to start with ( so even if your original image is gray, make sure it's in grayscale mode). Note, this is kinda moot if you save as PGN8 or GIF... but for something as textural as wood, I wouldnt go that route anyway.
2) You can lighten /darken and ad contrast with the level slider.. but I tend to favour curves. It offers far more control.
3) consider your bg dimensions.. 2600px@72px/in is awefully big, and is useless for mobile devices. How about:
1300px ( or so @ 36px/in?) and compressed at 40% jpg ( a lil blur might not hurt either since this is merely a page bg)