Mine does the same. One tire at 33psi is an issue, but the other 3 are ok...lol. Ram has a button you can press to relearn the tpms threshold on 3/4 ton trucks. I wish Jeep did the same thing.
I'm missing 2 as well. Can't decide to buy new Center caps or new wheels...lol.
I'm building 2 trailers, one for hauling stuff and one for camping. I can find matching wheels (like yours) for $100 so I'll probably just keep them and then buy center caps.
I have the Ram dash mount but haven't found a system I like yet when it comes to attaching arms and mounts. I hate the bulk of the ram arms. I'll probably order the bullet point arms and add my own phone and tablet mounts.
I did a similar thing but only 60%.
Mine goes under the back tray and is secured with the bolts that hold the tray down. I put a hinge just in front of the tray.