Hi Griz...
First off, welcome aboard! Congrats on that new Traeger! There's nothing much easier to operate than a pellet smoker. Just fill the hopper with pellets, set the temp and go!
I was gonna ask the same thing Al asked...many times, those big cryo-packed pork shoulders are actually 2 pieces of roughly equal weight. If it turns out that it's actually one whole hunk of meat, I'd suggest going ahead and cutting it in half. Much easier to handle and cook two 10 lb. roasts than one 20 pounder. This also drastically reduces the overall cook time...figure your time estimate based on 10 lb. hunks.
The rule of 2 hours per lb. is a reasonable guess for your first cook, depending on your cooking temp. At a "low and slow" temp of 225*, it may well take between 1.5 and 2 hours per raw pound of meat to get it done. Obviously, the hotter you cook, the more time you can subtract from that estimate. I generally cook pork butts (shoulders) in the 250-275* range myself...but I'll still allow around 1 - 1.5 hours per pound so I'm not rushed to get it on the table by serving time. I actually prefer to smoke pork butts a day or 2 ahead of time and reheat the day of...pulled pork reheats very well.
For your first try, I'd suggest keeping it as simple as you can...apply a healthy coating of your favorite pork rub, get it in the smoker, and let 'er ride. Some folks like to mop or spritz the meat at least once an hour, but I find it unnecessary with pork butts...and every time you lift the lid on that Traeger, you add more time to the cook by allowing heat (and smoke) to escape.
With a pork shoulder, don't concern yourself too much about how long it takes. Many of us say "it gets done when it gets done." Be more concerned about the meat's internal temperature (IT). If your don't already own one, get yourself an accurate meat probe thermometer. Your target IT for that shoulder is about 200* if you plan to make pulled pork out of it. Once it reaches the target temp, let it rest under a foil tent on your counter or in a cool oven until it has cooled enough that you can handle it without burning yourself (this may take an hour or longer), then just use your hands to pull the tender meat apart.
Many guys will then apply some kind of finishing sauce, although I personally usually don't. Here is a link to a very popular one:
http://www.smokingmeatforums.com/t/49892/finishing-sauce-for-pulled-pork
I know that's a lot of info to take in all at once...hope it helps!
Good luck! And remember...we love to see pics of others' cooks!
Red
