Poor performance after upgrade from Online 7.1 to 7.23

Greetings, We have two databases on the same rs6000 running AIX with the 7.23 Online engine. After our recent upgrade from Online 7.1 we experienced a huge performance hit. We, with the help of Informix support, found the problem to be a bad index in one of our larger tables. Since then we have discovered other, less critical speed problems that we have yet to get Informix support to look at. Can someone give me info on how to do this myself? I'm wanting to use the oncheck -cI command to verify the other indexes are correct, but i can't find any specifics on how to use it. Can someone help? By the way, this is a 'round the clock production system, so I must be careful. Thanks in advance for any help. RG