2004 grand prix gt 64000kms on it, is it ok to put STP injector cleaner in once and a while with higher octane ?

Yes. Injector cleaner won't hurt anything. If there are any deposits in the fuel system the cleaner should remove them. You may even want to consider putting a can in every three months just to keep things clean. Another issue that you don't want to forget is to change the fuel filter periodically.

Do you have any mods? Octane booster? Worthless and a waste of money. :lol:

If you use good quality top tier gasoline which has detergents in it you don't need any fuel additives. :grinno: