Any change in airflow may require an ECUTek tickle...the fact that the OE filter improved things may hint at this. Also bad fuel can stuff things up...in such cases it's best to run the tank to reserve then fill up with a new batch.
I suggest you take it to MMS (I'm guessing that's where the ECUTek was done) and get Steve to check the ratios...however you will have to delay this as Steve is currently away from work on sick leave for at least a little while.

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