That's exactly the way you have to use the brakes. You are using them to go ahead and slow down, or take your foot off the pedal. By "reducing slightly" the pressure you are in other words riding your foot on the pedal and not using the brakes.
I know it sounds like I am giving you a hard time, but I really don't mean to. I am just trying to help. You ought to drive a larger truck with air brakes. There is no in between with those either. When you are empty with air brakes, you are rolling or your head is going through the windshield.
