This was interesting work from Brian Sampson of BBallBreakdown that was published 12/30, when the Bulls were on a 10-2 run and before their current three-game losing streak. The cracks in the facade were there:
Their defensive rating since Dec. 8 is the second-best in the NBA at 100.6, which is an astronomical turnaround. Opponents also saw a significant dip in shooting by only knocking down 45 percent (10th) of their shots from the field, including 30.8 percent from downtown (second).
I warn you not to be too quick to give Chicago all the credit for this turnaround, as Lady Luck deserves a lot of it.