I own a 2013 se, it's got a flowmaster welded muffler and k&n airfliter. Recently my car broke down due to a transmission issue(not caused by common focus transmission problems). It threw a code and I had a buddy of mine read it for me the code was p0902, it was because of corroded battery grounds, after cleaning that up the car has been doing alright. How ever I have noticed a big change with the way the car shifts through gears. It feels like it's nervously shifting, and every once and awhile the car will jolt really hard before shifting. I have since ruled out a mechanical problem. It has to be something electronically I'm thinking the clutch actuator but I'm not sure(all fuses are fine and everything I'm able to check with my voltage reader is good as well), I just wanted to see if anyone could help me figure what the problem could be.