As the final step of our closet redesign, we installed a door from the upstairs hall into what used to be the master bedroom closet. This door install went a lot easier than the last 2. It was not a pre-hung door but it is also a lot easier to cut down the height of a slab door.
The inside required some drywall installation and patching, but at this point I am a pro at mudding. The hall and trim still need to be painted, but that is a job for when the windows can be left open.And now we know: when you are cutting down the height of a door before installing it, it is just as easy (and cheaper) to buy one NOT pre-hung and assemble it yourself.