I have a 2010 charger ex police with a 5.7 with 160,000 km (100,000 miles). Car works great under hard acceleration but stumbles a bit at first when I give it gas. I smoked the intake and there were no signs of leaks. I am wondering if our cars are known for brake boosters leaking vacuum? I do find the brakes a bit stiff at times so I am wondering if I am barking up the right tree. Maintenance items have been done such as plugs and air filter etc. Any input would be appreciated .