I've had a turkey in for 4 hours, at 250 (regular 3D). The turkey is currently at 147, but the box temp is at 217. It hasn't been higher than 219. Any thoughts?
The turkey is a large item (you don't mention the weight) and as such will be intercepting quite a bit of the heat from the element before it reaches the box temp probe. As the bird gets hotter, more heat from the element will reach the probe. If your bird is cooking satisfactorily, relax and enjoy.
If it is a non-D model, then your ambient probe might be the problem. Place it in boiling water and see if it registers around 212. Then place it in ice water and see if it's around 32. That would be the first thing to try. Let us know how that turns out. It could be other things, like your dial needs adjusting, an issue with the element, but you should start by testing the probe. Test both of your probes while you are at it.