My blazer has a 350 motor that runs really well when it's warm but seems to have the symptoms of a vaccum leak. It chugs when it's cold and when it's warmed up the exhaust manifolds occasionally glow(i've been told that is a byproduct of a vaccum leak), it also runs a little hot. Could these be cause by a leaky intake manifold? It is pretty wet around there but i'm pretty sure that's from the valve covers. Should I just replace the valve cover gaskets and see if that stops the leaks? There are no vaccum leaks externally which makes me think it could be in the manifold. Tanks a lot for any and all help.