Dave
A cold air intake might give you negative mpg gains but will help the hp.
I'm sure you know that air/fuel ratios fall into a narrow band and that a given displacement engine under load will require a set amount of fuel to maintain stoichimetric levels. Cylinder volume dictates the amount. So, a cold air intake will result in a denser charge in the cylinder and that will require more fuel. To maintain speed a set rpm is required. The increase in power will let you use a lesser throttle setting so you are still supplying the same amount of air/fuel in a denser charge as you would without the cold air. Thus no appreciable loss or gain.
The only way to improve milage is to lessen displacement, lessen load and have a fuel management system that will run the engine at the leanest possible a/f ratio for load conditions.
gonna dance, gotta pay the piper an a whole bunch of middlemen.