gas milage after catback install?

[wickedh3]

First time poster, been browsing the site for a few months.

I recently just installed a Bassani catback on my H3. Its the single muffler where the resonator was and splits into dual pipes over the axle.

My gas milage has gone to **** since the install. I regularly got 17-18 mpg with mixed drving. I am now getting 15-16.

I understand about having more power and keeping your foot into it too much, but after careful driving, increasing tire pressure to 38 psi and mostly highway milage, i cannot get the milage back.

Since these vehicles are drive by wire im wondering if something needs to be done in the torque demand tables in order to take advantage of the exhaust and efficeincy.

What are other people experience after installing there catback systems.