1999 Dodge Ram 2500 5.9L Diesel Seat Belts Locking Up

I have a 1999 Dodge Ram 2500. The seat belts were replaced last September (8000 miles ago) because they both locked up. Recently, they both have been randomly locking up and then releasing at various times. The seatbelt light will sometimes come on even though the seat belts are connected. The Dodge dealer could not duplicate this problem even after having the vehicle for over a week. I drove away from the dealership and within 2 miles and 3 stops the belts were locking up again. I took it back to them immediately to show them that it was locked up and they were still unable to explain why this is happening mostly because it is not sending a code to the computer to let them know what is defective. It is a Chrysler Dodge dealership that I bought the truck from almost 10 years ago. Does anyone have any suggestions?