Imprezinator's car did not show the same problems with the 2.2 block, 2.5 heads and stock 2000 ECU.
When you blew your 2.5 did you have the heads checked out? Some of the valves may be damaged and you are getting incorrect amounts of air in some of the combustion chambers...
You may have to bite the bullet and take it somewhere to check it out. Your motor shouldn't see such huge differences from left to right.
Let keep one thread open for your problem, so the discussion won't have to repeat itself.