Thanks all for your imput. I did increased the buffer size. I also changed the parameter file as in oracle note id:#93763.1 unfortunately none of above helped with my problem. I am guessing its resource and contention issue since our upgrade.
Amar, setting index=n is time consumming. I did create large rbs before the import and kept others offline.
MH, can you expanciate more on the followin:
Did you switch optimizer modes?
When was the last time the tables were analyzed?
Is Pluto aligned with Jupiter?