Performance issues with 10.2.0.4 database

 We recently upgraded one of the production(OLTP) database from 9.2.0.7 to 10.2.0.4. One of the important job from application end is running very slow in 10.2.0.4, it is taking twice time of actual(9.2.0.7).When traced the session in both 9.2.0.7 and 10.2.0.4, I can see execution plans are quite same. The difference I found in between both traces is in wait events, Db file sequential reads and Log buffer space events have dramatically increased. SGA size and logbuffer space size are almost twice bigger than 9.2.0.7, but still facing performance issues. Can any body help me.