UDS pork butt questions - (help!)

I'm at the end of my fourth uds cook, third time for pork butt. Here's my situation:

1st cook - pork butt on for 12 hours at temps 225+. never did get above 160 per meat thermometer. pulled from grill, rested for 30 minutes. Pork was done, tender and pulled easily. Also, best I'd ever had!

2nd cook - determined to hit magic 190 - 200. Started 4 am. cooked for 13 hours, temp never got above 160. Guests about to riot, so I pulled from grill, rested for 30 minutes. Again, pork was done. tender and pulled easily.

3rd cook (today) - put pork butt onto a 300f UDS last night at 9:30. set valves. checked at 3 am (250) and again at 6 am (250). I'm now at 15 hours and guess what? temp is still 160 internal! I checked thermometer with boiling water and it's within 5 degrees.

Am I missing something? I continually read of cooks around 12 hours, but I'm blowing by that and still not hitting temps.

Thanks,

Dave

PS. all butts bone in around 7-8 lbs.

Finally pulled off the grill at 2pm, 16 hours. Internal temp indicates 190. The probe goes in like butter, I may need a new thermometer. Although I'm pretty sure it's accurate, based on testing it in boiling water.

I believe that maybe, in an attempt to keep the lid on as much as possible, I'm not allowing the thermometer to reach max temp. I stuck it in and left it for a few minutes and it read higher.

Thanks for all the quick replies. I'll post a quick pic.

Dave,