One problem related to tank assembly has been reported for the 1999 GMC Sierra 3500. The most recently reported issues are listed below.
Fuel tank under negative pressure by apparent stuck valve caused fuel tank rupture. Happened twice. Gm engineers said no defect, apparently there is and no further communication would be provided. Fuel spilled out and was very dangerous, in my opinion. I am a degreed (msme) engineer. With an extensive auto background. Updated 11/15/05.