Hi Rjmchamp,
Congratulations on the new Bighorn and welcome to the Heartland Owners Forum.
There are 2 aspects to your PDI: learning what's what and how to operate everything, and checking that everything works. Take your time and don't sign the acceptance paperwork until you're satisfied that everything works, or for anything that can't be corrected on the spot, that it's noted in writing as an exception that needs to be corrected.
It's pretty easy to miss things, so if at all possible, you should arrange to stay at the dealer or nearby for a day or two so you have a chance to try everything while using the coach. Before signing, talk with the service manager (with sales at your side) and explain that if you find anything that needs to be corrected, that you'd like to bring it back and have it fixed while you wait (barring items that might need parts not on hand). That'll save you having to drop off the trailer and wait for them to get around to fixing it.
If one person can pay attention to how things operate, while the other videos the walk through, you can refer back to that video to refresh your memory.
Being new to 5th wheels, pay special attention to hitching/unhitching.
We have a number of owner-written user guides that may help you prep for the walk through.
Here's a link.