Have had this problem for several months. Finally found this thread, so I went out to my truck, straightened out the seat-cover straps, messed with the seatbelt buckles on both sides and middle, rearranged the toolboxes behind the seat, and no more airbag light on dashboard when the truck is running. Problem solved.
Considering how many people might be having the same problem, it would be nice if the manual outlined possible triggers for this warning light. It would seem that this is especially important when dealing with passenger safety.