1998-1999 GMC C3500 5.7L V8 CNG;. 1998-2000 GMC C3500 5.7L V8 GAS;. 1998-2000 GMC C3500 7.4L V8 GAS;. OE Equivalent Fuel Tank Cap;. Fuel Tank Cap;. Gates - Driven By Possibility. Two-way action pressure relief/vacuum relief valve allows fuel tank to ?.