ember is pretty spot on with how to activate hill start assist. Here's a post to the full criteria from GM:
https://www.camaro6.com/forums/showp...6&postcount=17
To the "need to push harder on the pedal" comments, it really doesn't take a ton of extra force. You just need a tiny bit more over what it takes to keep the car in place on the hill. If it's not activating at that point it's likely either the car's not in the right gear or isn't on a steep enough grade. 5% is a little steeper than most people probably expect. It's not meant to stop all roll entirely, it's meant to help in situations where the grade is steep enough that you can roll a decent distance in the time it takes to get moving.
I'm also not sure what the big deal with the electric park brake is either? Even if someone doesn't trust hill start assist, you can manually apply the park brake and then just drive off as normal when you're ready to go. These cars all (manual and automatic both) will release the EPB once the clutch is released and throttle is applied far enough while in gear. Only exception I've found to this is if I try to drive off right after I first start the vehicle it'll sometimes not work, but after running for 10-15 seconds it's always worked for me. There's no need to do a half park-brake hold or roast the clutch by keeping the car on the grade via clutch slip, there's two separate brake systems on the car specifically designed to do that now instead.