Just joining the community and thought we would start with something to share.
Here is a free iPad mockup PSD with smart object layer: 4912px x 3264px, 360px/inch and 83mb.
To replace the screen, double click the smart object layer to open it. Replace the contents with your screenshot, save, the mockup will update automatically. Enjoy!
The pack is under a royalty free license in both personal and commercial use.
Download here: https://goo.gl/Cgu3T9