My 2014 mirage mpg is much lower than normal. Please help!

[robertico]

Hello I have a 2014 Mirage CVT SE that I bought new. I absolutely love my little car.

I used to consistently get over 38 mgp in the city (often 40) and about 44-48 in the highway.
For the past year I only get about 28-30 in the city and 40 in the highway.

I religiously change the oil with full synthetic at the dealership, but I haven't done any other maintenance appart from tires and front brake pads.

When I turn the engine on, the engine does seem to have a different sound. It doesn't seem in tune.

My car now has 73 000 miles, and I have never done an engine tune-up.

Could that be the cause of the decrease in fuel efficiency of my car? I was recommended to change the transmission fluid at the dealership. Should I do it? or what should I be checking or doing?

Thank-you for all your help =)