I'll be prepping my Traeger to get ready to sell once the Bull comes in. Just read a review that the weber grill cleaner (spray bottle) was recently rated better than others.
I have a steam machine, so I think I am probably just going to steam the inside and get as much crud as I can out of it.
For grate, I used a mud tub and mix water and simple green in it (10:1 or 15:1) and let them soak for about 6 hours. Crud comes right off.
You might loosen up the crud with some Simple Green aerosol BBQ cleaner first before your steam cleaning. It works on all the "soft stuff" pretty well.