I have found the cruise to be acceptable but have had better on slopes. I think that possibly the torque of the engine (and gearing of some transmissions) has a lot to do with the ability of the cruise to hold speed, especailly as you have inclines. (Big V8's don't lug down easily)

I've found on steep slopes uphill with the cruise set at 70 that the speed may drop down below 65 and then the accelerator comes on with a vengence and the PSD starts making a lot of noise (sounds like a normal car down shifting and kicking in the 4 barrel). Going down a steep slope I find that at 70 I have exceeded 80 mph and had to use my brakes as it would not hold me back (not that I really want it to)

However for 95% of my long distance driving (flat to mild slopes) the cruise seems well fitted for the hybrid system giving good FE results. I was afraid it wouldn't allow the ICE to go to the 60 mode like I can do when I lift my foot but the cruise sits at FE60 a lot on the interstate for me.