If I have learned anything on this forum it's from folks that have used their Cookshacks way more than I have mine.
One of the key lessons when using a probe with either pork butt or a brisket is that those cuts have pockets of fat that make getting an accurate read pretty tough. You have to be very careful to place the probe into a section of the meat that has no fat, not an easy job whether it be with the stock probe from Cookshack or a probe for something like a Maverick 732 (pretty good unit).
But let's see what other users chime in with.
I think if your stock probe is getting close to your target temp it is time to put the adult beverage down and take a reading with a digital quick read thermometer such as a Thermapen or a CDN DTQ450X