I run a similar setup, ie....22.5 WSM with a digiq dx, Maverick remotes, all thru guru eyelets. I started with the ET-73 and it was way off of the Guru pit temp....25-30 degrees or more. I called Maverick and they sent a new unit. Same thing with this new one (and new probes) and was way off once again. Boiling water and ice slurry tests showed Guru and Maverick were both fine and in agreement. I sent Guru back for calibrations, came back with reports of being fine but once again, Guru and Maverick did not agree. I ordered an ET-732 figuring a new model may work. Same THING again.
Well, I was at witts end here. However, I finally figured this thing out. My probe wires were dangling down the outside the WSM body and making contact with the unit. Of course you cant help the probe leads touching as they go thru the eyelet, but dangling and making contact with the body was causing heat conduction thru the shielded probes.
Try to keep the probe wires off the unit as much as possible and it will agree much better.
I still notice that it takes an hour or so for both devices to agree as they come up to temp. Sooner or later they will be about the same, at least in my experiences.