Bad gas mileage after engine re-build

I own a 2011 Elantra Limited that I bought a little over a year ago with about 92k miles. About 3 month ago I started to to have ticking noises in the engine. Called dealer, drove car to dealer, dealer says short rods damaged and I need engine rebuilt. At that time I had about 101k miles. Fortunately the rebuild was covered by the extended warranty I bought (saved me 5 grand). My MPG is since the rebuilt nearly anywhere close to what it was before. It is around 15% below what it used to be. When I called the shop they said that that is normal and would improve to old levels after about 3-5k miles. Now it is about 3k miles and still not where it used to be. I barely make 33-34 MPG on a pure highway trip. This is what i used to have on my short work trips.So my questions to you guys. Is that normal that after an engine rebuilt the gas mileage drops that significantly and stays like that for a long time?

Thanks,