Both engines share almost same engine foundation layout but the ECM system and transmissions are different 4 gr has 4 speed dual convertor lockup mechanism
Where as 3 gr has 5 & 6 speed with dual converter lockup system so if some one is using only 3 gr engine with 4 gr ecu it's not worthy and if the ECM along with transmission is swapped and working properly then it will be a more robust swap with lot of torque and lowest cruise rpms at highway along with better fuel economy