parallel query tunning

Hello experts,

                       One of our data extract job using external table is taking more than 2 hours in production.I am trying to tune that statement in production like environment.There is a large portioned table called reading for which query reads through each partition and as per awr sql report it reads 685G of data.I tied to force local index pk_reading  which has index on column NODEID, ENDTIME, READINGGROUPALTERNATEKEY but query ran for 12 hours.I am attaching qwr sql report with hint and without hint.Please tell me why my index hint is regressing the query?