CBO performance between 7.1.4 and 7.3.2.1

I just installed oracle ver 7.3.2.1 on a dec unix box. 7.1.4 already resides on the same box. I created an identical database for each version from one of our production systems. Both databases has stats for all tables with choose as the optimizer mode. I took three sql statements from the sql cache on our prod system and ran them through the explain and tkprof on the two versions of oracle. The 7.1.4 database performed approx 50 % better than the 7.3.2.1. The explain showed that the 7.1.4 databased used different indexes than the 7.3.2.1.

I was always told that CBO does not work properly in any release prior to 7.3. Has anyone else noticed a performance loss on there applications after migrating to 7.3 from 7.1? In my situation 7.1.4 is obviously making better decisions on an execution path than 7.3.2

note: both databases have the same init parameters and is using the same hardware and both have new stats generated

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