There are many things that can effect temperature readings between different thermometers.
We must bear in mind that we are dealing with consumer grade electronics and not scientific measuring equipment capable of detecting nano changes in temperature.
With consumer grade electronics there is always a give and take in the design and the selection of components to keep the price affordable to the targeted consumer group. Different components, materials, and manufacturing processes will yield different products which will operate and respond differently to the same environment. Differences in materials used in the manufacturing process will also effect how temperatures are sensed and the time it takes to recognize that change and process it to the digital / analog display.
Two thermometers made by separate manufacturers can yield differences in readings even if both thermometers were calibrated on the same test equipment. Components used in the manufacturing process can cause some thermometers to take a substantial amount of time to display the correct reading. Some cheaper thermometers may take up to 3 minutes or more to register the proper temperature, while other more expensive thermometers have a very fast response time. There will also be differences between thermometers due to their reaction times, placement in the cooker, placement location in the meat, and even how the sensor responds to the relative humidity.
Placement of the pit probe near the meat or closer to the sides of the cooker can also reflect a cooler temperature reading.
If I had to trust one over the other, I personally would choose the Guru....
You can also try to reset the Digi-Q DX2 to factory defaults....
Humphrey's DownEast Beast W/BBQ Guru