Well, calibrating your Maverick is easy to do. Water boils at 212F so you can easily check it that way ... if nothing else it's good for some peace of mind.
You can pick up an inexpensive instant-read thermometer (less than $20 bucks); this is great to use with foods like ribs where a meat probe is difficult or impractical. The chamber probe should show variance based on the thermostat cycling the heating element on and off.
Ultimately, once you've got good pull back on the bones you're fine; 145 is the magic number for food safety and if you're seeing caramelization at the 2 hour mark you're likely okay ...