Looking for some feedback on Reviva Engines. Last year I replaced my factory 7.3 Powerstroke with a Reviva remanufactured (Drop-In) 7.3 Powerstroke in my 1997 F350. I had a couple of small issues and Reviva took care of them under the warranty. Now I'm having an issue with the fuel mileage. At first I seemed to be getting around 17 mpg; now I seem to be getting around 13 mpg. I have checked for fuel leaks and haven't found any. Any ideas on what the problem could be would be helpful.