2018 LT cruise control does not appear to control speed adequately

I have a 2018 LT, when setting the cruise control you expect it to be within an acceptable range and it does on flat surfaces. However even the slightest decline will cause a 5-10 MPH difference and it just doesnt seem right. No other car I have had does this (had an 07 LT and it worked great). There are many areas near me that are 30 MPH and I like to set it so I don't get a ticket. I can go anywhere from 28-45 on that stretch, which is counterproductive. I am not sure if this is because its a 4cylinder and my old was a V6 but it just is unreliable. Anyone else?