Are there separate fuses for each window in my 2007 Nissan Titan?

To answer your question, no, they all use the same fuse. Since the Titan didn't do a "refresh" of the first generation until the 2008MY, I'm pretty sure your Titan should be the same as a 2006MY. Here is a fuse diagram from a 2006 where you can find the 50A fuse which supplies the BCM and windows (ignore the red circle ... the fuse is up and just to the right of the red circle; it's marked "BCM/PWR WDW"):

Usually when a window starts moving slowly, then dies altogether, it's due to the motor going bad. If the motor goes bad, you need to look at the regulator, as it can cause premature motor failure. You can attempt to power each motor individually, but usually it's just better to replace them.