Before you jump to a PID and what it is, let's check your Maverick probes. Put a pan of water on the stove and bring it to a boil. Water boils at 212F. Stick just the tips of your probes into the boiling water and see what your Maverick reads. If it reads 212 or a couple of degrees either way, your probes are fine. The constant 40 degrees difference is odd in my opinion. The BDS is known to be inaccurate in registering temps from the tower but a constant 40 degree difference is something I have never seen. Not saying it doesn't exist, just saying I have never seen a constant difference like that. As the meat comes up to temp the heat swings should lessen.