Cruise control accuracy downhill & uphill

Just bought 2017 Ford Edge & the cruise control is very accurate going downhill or uphill within plus or minus 1mph.  On the 2013 avalanche, going downhill it speeds 5mph more then what the setting is. Going up hill, it' loses more than 5mph . Is this normal for the cruise control?

With GM, yes. 

Mine is pretty darn accurate going uphill - it doesn't downshift or brake going downhill which means it will speed up.  Frankly I like it that way.