At 375 ~ 400, you would most likely have to have a lot of extra liquids for the thing to swim in, to keep it from being really dry.....
There's a set of scientific mumbo-jumbo that occurs to have the fats & connective tissue break down / disintegrate that needs "X" time to work.......it seems to work better @ these lower temps; read: given enough time..............
I usually run approx. 260, for as long as it takes; each one is a bit different & so takes different lengths of time.........
I don't usually stop cooking & rest until around 200 internal, the rest is: foil wrapped, then towel wrapped, then into a dry cooler, usually for at least 2 hours.....the rest period, in my estimation, makes a bunch of difference......
After that being said, I've had charcoal setups that kinda ran wild while I was sleeping & gone at 325 ~ 350, then being done quite a bit sooner..........
It's different, easily enough different for me to tell & need to add something to keep the moisture up until & at serving time.......never really wrecked one & a lot of people do them @ the higher heats, but it's tricky & the faster things are moving, the less time you have to correct any problems........just plain makes me nervous at the higher end of things,......
You can run up to say, 175 ~ 180 internal & rest a bit & slice it, that way, you're a bit past the fat breakdown point of about 160~ 165............pulled COULD be as low as 190, but usually is 200 or a bit higher....
I like a ten pound, bone-in shoulder, plenty of fat to keep it moist, plenty of surface to get a bunch of bark & when then bone slides / breaks free of the adjacent meat the tissuses have broken down just right.....built in pop up timer !!!!