I am currently have the exact same issue with my 2010 STI, just did a 20g Turbo, 1000cc ID injectors, dw65 fuel pump, FMS FMIC, ect, everything went great with the tune drove the car home no problem. woke up the next morning and went for a canyon cruise up and down the canyon was great. Once I got on the freeway I put the car in cruse about a 4 miles later it thru an engine light. I got off the freeway and stopped at a local pep boys and had them run the code, came up with a system to lean bank 1. Called the tuner he said clear the code should be fine. Well from that moment on it stutters really bad from 2700 rpm to 3000 rpm in every gear every time. Even if cruising on the freeway at a constant speed if it is in the 3000 rpm range it will stutter the entire time until you either speed up or slow down out of that Rpm range. We did a log on the car and numbers were all over the place based on where we were on the dyno. Car was pulling like 6 deg of timing through out the rpm cycle. One other thing was that the intake temperatures were really high. When we were on the dyno "in a cool shop with the bumper off and fans blowing the whole time " intake temps were only reaching about 120 ° but when logging on the streets with out side temps at about 103° the intake temps were getting up over 200°. So we first checked for leaks air/fuel and everything looks good. Next we are going to work on temperature by re routing intake/intercooler pipes because the current set up has the hot side pipe running on the intake side so we are switching them around. I also orders some new headers and up pipe that I took to be high temp ceramic coated . So once this is all complete I will chime in again hopefully it fixes it.