P0442 Gas Mileage
 

Hey guys I'm back. Just picked up a '10 Yukon Denali Hybrid. Traded in my '09 HyCon and I've owned a Honda Pilot, good truck mechanically but poor quality design (everything rattled in the interior) and VERY boring. Then I "upgraded" to a 2012 BMW X5M. If you don't know what it is... 550hp twin turbo suv, and I say "upgraded" because it was in the shop maybe 10 times the year I owned it.

Now to my problem: so I've been driving around with this code for a couple weeks because between work and my wife's schedule I just hadn't had time to get it fixed. So they found 2 leaks with the smoke test, replaced the parts, $1000ish later and the code is off but... my gas mileage has plummeted! I'm pretty conscious about what MPG I get on certain roads and there is a noticeable drop. For example I was getting 30-31 on this long stretch slight downgrade and last couple days it won't crack 26. Any ideas?