I am purchasing a vaccuum tester and Kent's book becuase I likely have a vacuum problem based on these issues: Automatic Transmission shifts too early(fluid was changed); door locks sometimes work -usually they don't; Left front disk brake kicks in 1/4 -1/2 second after right. Lines appear to be in good shape..as well as vaccuum levers on valve cover- but I am thinking could be a main check valve (or other valve) problem. Not sure whether to do the vaccuum pump rebuild kit yet - until I read the book anyway. Anybody else experience these symptoms?