Mr Coach,
Well, you said you tried the cruise control, right? And it had no effect? Not sure where to send you now as, like other posters have replied, ours too works with the cruise. But, you don't have to have the engine brake off on ours. The cruise doesn't care whether the e-brake is on or off. At least that's the way it is on ours.
Now, ours is an '04 Itasca Horizon with the 330, C-7 CAT. And, yes, we do have the "Smart Wheel" so, on otherwise equipped coaches, i.e. non-smart wheel, Cummins engines, etc. I'm not sure of the procedures for idle step up on those. Be sure to let us know what make and model of coach you have so, if someone's got an identical coach/engine etc. they may have an answer for you.
Scott