Loosing Fuel Efficiency

What is your question?

When i purchased the vehicle 2 years ago. i never experienced loss of speed but in the past 4 months ive been experiencing this problem and i dont know if it just needs a tune up or if the electrical system could be bad. I have it in the shop right now and no codes come up. So im thinking about taking it to the dealer maybe they can find the problem. If anyone has any suggestions i can really use it. thanks