fuel saving chip?

Is there anything out there such as a performance chip that would allow, any car to have some of its cylinders shut off until you reach a certain speed for fuel economy. I know some of the chevys out there have something like this, and I know the V8 dodge chargers come with a multi-displacement system, but I wanted to know if there was anything that could do the same thing for a jeep.

Just a few days ago, there were a few threads on this topic...