I have a 2015 Gt premium automatic ( not stock ). I can’t accelerate pass 20 mph. No check engine lights and when I use paddle shifters I only can go up to 3rd gear 4th does not work neither does any gear after 4rth. My sct device doesn’t pic up any codes wrong with the car but I plugged my friends codes reader in it gave me 6 codes. I researched all the codes and still can’t find a solution! Almost like my car is in limp mode with not check engine light at all! Need help asap as this is my daily car!