Coming up out of posture during the downswing is a common fault created by a lack of strength in the glutes (buttocks), try stretching and strengthening them by lying on the ground with your knees bent and lifting your hips and buttocks off the ground for ten seconds
Steven Bann’s philosophy on the swing mechanics and practicing under pressure
Take a more lofted club because the hill will lower your shot trajectory, then move the ball back in your stance to where your practice swings made contact with the grass and open up your left foot