Pork shoulder picnic on MB 2 door

I've had my smoker for about a month now and I've successfully smoked corned beef, while chicken, and ribs. Today I went in for a pork picnic and had two 7-pounders. And they were too big to fit on the same rack so I put them on separate racks about 6-8 inches between them. I had the temperature probe in the top one figuring when that one hit 195 the bottom one would definitely be done. Well the top one stalled at 145 at 12:45pm and only rose to 160 in very small increments and was still at 165 at 7pm! It had been in the smoker since 6:30am so I figured it would take 10.5-12 hours tops assuming 90 minutes per pound. I held pretty steady between 220 and 230 for nearly the entire cook until the end when I had guests over and had to crank it to 325. After 2 hours at 325 I instant read thermometer the bottom one at 200 so I pulled it out. Tented with foil and it had great bark and pulled beautifully and if this was the only one I made I would have been happy. However the top one was still at 176. At 325 it took another 90 minutes to get to 190 and I pulled it. It was definitely not ready as it was not easy to pull and ended up dry and shredded. The skin was definitely not bark like and most of it was tough and almost like jerky. At this point it was over 14 hours in the cook, 3.5 of which were at 325 degrees. I felt as though I had had enough and was ready to cut my losses.

Can someone give me some insight on what the hell happened here? It seemed like 4 hours in the smoker and only getting to 145 was a little low but I just don't know what to do differently. I thought about crutching at 155 which might have helped but a lot of advice said not to bother if you've got the full 12 hours available to you. I was planning on the pork being done at 6:30pm (12 hour cook) and 30 minutes to rest before pulling.