I don't prep a thing, get the fire going, pull the butt out of the cryo, rinse and dry, rub it down, and cook it till probe tender. Prep is "extra work". And it's not needed to put out a great product.
For comps, yes prep is important. For backyard cooking? Nah. You could of prepped that piece of pork for 3 weeks, but in the end, it would still be undercooked.
But back on topic, I agree with everyone else. It sounds like you removed it from the heat before it was "done".
Rescued 22.5" OTS. SJS Mini-WSM. HEB briqs (rebranded Royal Oak). Pecan/Hickory/Cherry/Apple/Peach woods.
2016 Fuji Absolute 2.0 LE (for burning off all the great BBQ)