One problem related to rear seat belt has been reported for the 2003 GMC Safari. The most recently reported issues are listed below.
Purchased booster seats for our grandchildren. A certified inspector showed us that all four rear seat belts do not lock when pulled quickly indicating that the seatbelts would not restrain the child in an accident (or an adult either). Took the vehicle back to the dealer. Dealer claims the seatbelts lock when you brake hard, but are not made for children's booster seats. We are under the impression that vehicles made after 2001 had to have the appropriate seatbelts for child safety.