Libo,
You know my position on the Auber. Although I don't have a model 3, I have used 2 models of the Auber on the model 1 and 2 smoker, with similar results. If the unit is tuned properly, you should not be experiencing large temp swings, despite what you were told by whoever you talked at down at Auber. Maybe those swings are common in the looser, less-insulated smokers, but the common experience with the SIs is tight temps. If we didn't get that, no one would be using one today! I got +/- 10ยบ with my stock controller!
Let's see what happens when you get your replacement unit.