Personally, it sounds to me that the car was busy relearning it's values... I.e. crisp performance initialy would be over fueling, running rich. The values would have slowly started to correct/ rebalance thus starting to run lean before eventually settling at a relearned trim. I think you jumped the gun and had a knee jerk reaction to the learning process before it started to settle.
I've seen this many, many times over the years with simple installations of induction filters and performance exhausts. Pre fuel injection days it wasn't as dramatic an issue and tinkering with fueling/airflow was an art in itself but with immediate effects. More modern cars will resist everything you try in order to optimise their given fueling/ignition map then settle eventually to a happy medium.
Another alternative is a rolling road tune up with your new items installed for virtually instant results. Down side is this costs money but you'll get far better results than you will ever get with a factory map and just new items fitted.
Look at it this way, the money you will save in fuel economy over a year once it is all matched will pay for the tune up initially.