Its really difficult to understand what slow is to you. If you want more bottom end pull, the easiest way is drop the front 2 teeth to a 15T output shaft.
However with dropping 2 teeth on the front the top end speed will be reduced to about 188MPH or 302KPH
Maybe the engine needs some plugs?
How many miles on it?
Maybe a ECU upgrade with RCK2 and HP Power kit enables? I do those for the 10-14 as well.
CLONE ECU's are going to rule the world - ECU A against ECU B
All Keys Lost programming available FREE for some Forum members
Cut keys and programming available FREE for some Forum members
ECU to Cluster Matching with 200MPH available FREE for some Forum members
Add / delete DDC available FREE for some Forum members
All done here in the USA now and you dont have to ship to Poland