Gas Mileage

[dsmghost]

Clean your throttle body and run an intake cleaner through a vacuum source. Change your spark plugs. Air filter dirty? If your o2s are bad enough to effect fuel economy it would set a code and turn on the check engine light. Make sure your tires are at least 30 psi.

For the funky shifting do like said above, flush the trans fluid and replace filter, if you can drop the pan and replace the filter on a Kia Rio idk.