From the Gasoline and Diesel update, plus EIA:

Note that diesel was only slightly below prior peak, despite the fact that Brent was lower than it was in March or June.

Front month futures for Brent (NYMEX) is $92.38 as of 3:23PM CT. I don’t see a reason for Brent to go down on a sustained basis, so o particular reason for a drop in diesel.