79 c10 vacuum leak please help?

[c10Sleeper]

Hi my name is Kori well until recently my truck was running fine i bought a new master cylinder and booster and had a mech install it when i got the truck back i it doesn't stay running or idle i have to keep giving it gas and keep the rpm above 1500 or it will stall and shut off. i figure its a vacuum leak because of 2 reasons 1 the booster that was installed which deals with a vacuum hose but that hose is secure and clamped to the manifold and reason 2 is because when i give it gas i hear a faint whistle. the whistle is not the fuel pump going out this i know because i just replaced it 20m ago and the problem still persist. plz help any advice is helpful and