Your requirement is to synchronize The G/L Class value between Item master, Item Branch, and Item Locations, correct?
Issue is that G/L Class for the same Item / Item-Branch may have multiple values - some of which may be valid and some of which aren't.
Typically the discrepancy that can cause the most headaches is when G/L Class in Item Branch has one value and the corresponding Item Location records have a different value(s).
I don't know if there is now a standard UBE to reconcile/synch this but years ago we wrote a custom UBE to synchronize our G/L Classes in these three tables. Changes to a Item Location (Inventory) G/L Class generates G/L transactions as needed to keep the G/L in synch. We have this run on a batch basis nightly.