May be these are the answer to "요즘 어떻게 지내세요?"(How are you these days?) and both mean the same thing. In Englsh, A : How are you these days? B : Nothing Special. / Not bad. / So so. / ("I'm fine." means almost the same I think.) 늘 똑같지요, 뭐. -- Nothing special. 그럭저럭요. -- Not so bad, not so good.

늘 똑같지요, 뭐. Well, it's always same. 그럭저럭요. So so. *both are semi- formal form :)