I think someone else said it already but from my experience, the bigger the engine the better the following technique is. Go heavy on the pedal, get up past the speed you want to go, and coast. Rinse repeat. This works especially well with the Hemi's MDS cause it almost always comes on when you're coasting. Basically, if you have a "wider" speed range, where you're fluctuating between say 58 and 74, that will do better than just hanging on the pedal trying to keep a consistent speed that's somewhere in the middle of that range.
I had a couple of V4 vehicles, and a couple of smaller volume V6ers in the past, and all of them did better with mpgs on cruise control. But on the larger V6 (3.6L Pentastar in my JGC) and the two V8's I've had (4.6 in a Mustang GT and my current Hemi 5.7), cruise control was/is worse.