No brakes on my 440

I have a 440 on my dart and it doesnt stop..... i use a vacuum gauge and see that my engine no produce more than 5 inches of vacuum...... i use the vacuum of other car with a hose to check my brake booster...and my car stops great.

I dont know what is the problem....a friend tell me that i need to replace my intake manifold gasket (there is a leak!!!!!!)..... is this correct.....

Thanks