For the OP - just wanted to offer a couple cues I've liked in my experience. Just after you hit the bottom and rebound up, thinking "drive traps" into the bar helps a lot. Something I've been playing with lately is actually sort of thinking a high bar cue even though its a low bar squat. Once you are absolutely sure you have figured out hip drive and you are sure you are bouncing off your hamstrings at the bottom, I've found that thinking "hips forward" on heavy squats keeps my back angle from deteriorating so much. For me, my hips were going up and backward after the rebound, causing the good morning tendency. Just thinking "hips straight up" wasn't enough of a cue for me, so I found that thinking "hips forward!" right after the bounce - picture what it looks like to finish a heavy high bar or front squat, getting your hips more directly under you - actually balanced the good morning tendency and equaled out to a well-maintained back angle and minimal good morning on heavy reps. I wouldn't recommend this to everyone because it can easily be taken too far to the point of leg pressing the weight and taking the posterior chain out of it, but a good balance can be found. Hopefully that helps.