My lady friend has a 2014 Chevy Cruze 1.4 Liter that will downshift when not needed, and the car will not go above 63 MPH. It has about 74,000 miles on it. According to the owners manual it is due for a tranny fluid change after 40,000 miles, but should this cause these problems? It is giving codes for turbo and fuel issues. Her son and I changed out the faulty, noisy turbo last week and the turbo is running smooth, the car starts properly, runs smooth without missing.
Please post what codes you are now getting. When attempting to drive over 63 MPH what are the RPMs? I think transmission shift points are controlled by the computer system.