Check if any one for the rollback segments HWM is much-much higher than all the others, check for the optimal storage parameter.
From v$rollstat , check for extends and aveactive size , if high , increase rollback segment size and tablespace.

From v$sysstat , check consistent gets and db block gets and from v$waitstat check system undo block wait , if ratio is higher than 1% increase rollback segment size and tablespace and rollback segments.

thanks
GP