2002 Chevrolet Blazer wont crank up right

We got a intake gasket replaced now our truck won't crank right once crank up it drives fine but it don't won't to crank like it's not getting enough gas or battery is low but it's either one of those problems the machanic that worked on it tells us one thing after another all I want to know is What's wrong with it when we simply took it to get a leak fixed please help me