I'm not at all familiar with your type of cooker so this may or may not be "right on." A lot of folks, including myself, feel it's best to use a heat shield for "low & slow" cooking, aka indirect heat. Some use foil, some a water pan, and my personal favorite, a 12" Terra cotta platter covered in foil (look at Home Depot garden dept.) These make a great, heat shield, add mass to control temperature fluctuations and double as a grease pan.
I use a ceramic smoker and the temp never varies more that 5°, and most of the time, it's closer to 2° using the method above.
The Probes. All probes suffer a common weakness and can easily be damaged by the 2 deadly probe sins.
Sin 1: If you submerge them in water, they will die. Maybe not at first but as surly as the sun comes up, they will die.
Sin 2: The instinctive way to clean a probe is to grip it by the probe, spray some cleaner on it, and clean the probe and the wire connecting it by pulling the assembly through the cleaning rag. Wrong!!! This puts pressure on the delicate connection and very often renders the probe worthless the first time you do it. Grab it by the probe and clean the probe only, gently wipe the wire only when holding the wire. Having replaced many before learning about this, I consider myself a Dr. of probe replacements. Thankfully I learned on the less expensive Polder probes. ( I started buying these in bulk and have links to best pricing)
Since only the tip of the probe is reading the temp, I cover the the top portion of the probe up to about 1' of the wire in foil. That makes gentle cleaning possible. And I clean with a light mixture of Clorox bleach and water, just in case a germ might be around sampling my pork butt.
If you're sure your probe is bad, and it sounds like it is, and assuming you did not commit sin 1 or 2, call Rock and get a warranty replacement.
