For your front doors, you need these https://www.ebay.com/itm/50-Pcs-Ret...evrolet-NEW-/162212695578?hash=item25c4a14e1a
They do come all together, so you will need to pull the retainer off the bottom, set the pins in your door panel and pop the retainers in your door.
For my rear barn doors, I needed these, not sure if you have the same with your lift gate. https://www.ebay.com/itm/GM-GMC-Sie...153057-/251778510069?var=&hash=item3a9f2b2cf5
Spend a few bucks and get a panel removing tool from Advance or wherever. It will save you a lot of time and energy and keep you from busting the retaining spots on your panels.