7.3.2 vs 7.1.2

Hello.
I'm just going to upgrade from 7.1.2 to 7.3.2 and found that some
of my queries performing on 7.3.2 much slower than on 7.1.2.
For example, pretty complex query that takes 3-4 seconds on 7.1.2
now takes about 1 minute on 7.3.2.
EXPLAIN shows the pretty same total query cost (49000 on 7.1.2 vs
56000 vs 7.3.2, but 7.1.2 didn't calculate some subqueries).
What I did: make the dump from 7.1.2, load dump into 7.3.2,
tune postgresql.conf parameters like in 7.1.2, vacuum analyze.
Why is it take so long ?
P.S. Of course, I can show the query.
--
Eugene Fokin
SOLVO Ltd. Company