Having seen exactly similar situation in my most recent project, I can tell you that AIX 6.1 needs a fix from IBM.
I had investigated one place where they upgraded about 10 databases along with AIX at the same time. I found nothing wrong with the database all calls were served but in my report I had indicated that there were delays from OS and that those can be confirmed by system engineers only.
Please note that IBM, Informatica and Microstrategy experts were investigating already while I reported. My repport was complementary second opinion and they were not bound on.
After a week I was told by the project lead that IBM had found a bug in AIX and after applying a fix all was working fine.
Please do not take my story as guaranteed direction, but may be you can come to same thought via your own investigation.