Not sure on the GM, but it could possibly be part of the sending unit/fuel pump assembly in the tank. Look carefully at your fuel rails and see if there is both a incoming fuel line from the tank and the return line going back. If you have both lines, then somewhere under the hood is your regulator. If you do not have a return line, then the regulator is in the tank.
I have a Saturn ion with the 2.2L ecotec that is used in other GM cars. The newer ones like mine (2006) has a returnless system so there is no external regulator.