Mad,
Just did my first pork butt last week after many rounds with ribs and briskets which all turned out awesome
I experienced the exacat same thing with the pork butt, put it in at 4:30pm at 225, at 6pm it was at 129 degrees, I thought sweet! pork before bedtime. well at 7pm it was at 150, 10pm at 159?,
2am at 166!! I gave up, turned the smoker down to 190 and went to bed. at 4 am it was still at 168 so I cranked it back up to 225 and cried uncle. Frankly didn't care if it came out at all at this point. well at 730 AM, low and behold it finally reached the 199 mark! after wrapping and resting it pulled and tasted awesome. but man it took forever.
If I would have done this the first time out of the gates with the smoker I would be just as frustrated as you are, but fear not, for some reason those 3 LB pork butts can be just that, a pain in the butt
Try the recipe in the archives for the brisket, there are many but I've used the one by Arron brooks on a number of small flats, followed it to the letter and took the flats to the 195 internal mark before wrapping and resting, they ALL rocked!
The only insight outside of the recipe I can give you is do the flat fat down, it seemed to keep it from drying out better.
And do get a remote thermometer, keeping that door closed is huge.