On my recent model F150 there's a very handy feature: "Tow/Haul" mode. It changes the transmission shift behavior so that touching the brakes makes it downshift and STAY downshifted (and doing it again downshifts another step on the many-gear-ratios transmission), while touching the accelerator lets it shift back up. This is GREAT for long downgrades in mountains, even if you're NOT towing.
But it doesn't interact well with the cruise control. The speed control raises the throttle setting to keep you from going under the setpoint. But when you're over it just goes down to idle and lets your speed runaway. Touch the brakes to enable engine braking and the cruise control disengages. No automatic speed control for YOU on the downgrade. When the grade starts to level out the speed drops, and even before that you're back to watching the speedometer and doing manual adjustments,
Result: On mountain roads you're constantly disengaging and re-engaging the speed control.
They should integrate the two: When tow/haul mode is engaged, the speed control should send downshift signals to the transmission to control too-fast as well as too-slow conditions.
When tow-haul is on the speed control should signal the transmission to downshift when necessary, to keep the speed from running away and requiring the driver to brake. (The speed control's acceleration when too-slow will handle the upshift correctly.)
You'll still have to touch the brakes or tap-down the speed setting for curves and other locally slow zones. But then you'd just hit "resume" or tap-up the setting. Meanwhile the automation would handle the non-exceptional condition of preventing overspeed and runaway on downgrades.