Leaking valve cover gaskets affect mpg?

Anyone know if leaking valve cover gaskets on a 5vzfe affect mpg. Would this affect the vacuum on the motor, thus the fuel atomization in the engine? I recently replaced leaking intake manifold gaskets and valve cover gaskets on my tahoe and it made an improvement.
Not sure how this motor works with its pcv valve system. I was not able to locate the pcv valve to test.

 

PCV valve should be easy to find- on the valve cover.

Also, get a socket and snug up your valve cover bolts. Thats what I did on mine when I bought it, and the leaking stopped.

 

PCV is located on the back of the valve cover. Snug the valve cover bolts lightly, you don't want to break one off. This will stop the leaking.