transmission engagement observation

Jul 20, 2017
Vancouver Island
In my automatic 2001 D2, moving the gear shift leaver from Park to Drive sometimes does not engage. I notice a difference in brake pedal pressure before I more the leaver. On first try, the brake pedal pressure is less and the leaver does not more. On the second try, there is more pressure on the brake pedal and the leaver moves into drive. The amount of brake fluid is fine. What is going on?