Well, I'd first reset the computer and see if that helps. It takes a whle for the computer to reconize the change. You might also try to clean up the TB while it's off. Take off the sensors and clean them.
The 2.5L does not do too well at WOT. You'll want to state at what RPM this is happening at. It will bog if the engine is turning too slow although I've never had it backfire. If the RPM's are up, it shouldn't bog too bad. Gas mileage will suffer and performance isn't that great though.