Looks like a project similar to what Japan did with the F-16 being turned into a Mitsubishi F-2. S. Korea is turning an F-35/F-22 into their own version to suit their own needs, minimizing expenses and maximize the efficiency of their fleets.
Also making sure you trim properly can be a lot easier to takeoff. Place 4-5 degrees right trim for rudder, 0 for ailerons (unless you have crosswind) and 2 to 4 degrees Nose Heavy (NH) for Elevator depending how much fuel you have on board.
AFAIK Prepar3d is like FSX on steroids. Its a lot faster and less buggy, but it still resembles FSX.
You need to convert FSX addons through prepar3d SDK for them to work.