The GTR cars are not suitable for drifting. They are completely the wrong type of vehicle for this. There is one element that can not be overcome: steering lock. No matter how easy you make the car slide (not easy to do consistently on slicks anyway) you will not be able to produce a good angle because the steering range lock to lock is way to small. IRL drifting cars are heavily modified to suit their purpose. The GTR cars can be considered to be heavily modified for racing.
The GTRs are unsuitable for drifting. It is a waste of time to bother trying to force these cars into such an unnatural action.
Hope this saves you from frustration and disappointment.
To add to what Gunn said, you can drift the FXR somewhat easily, i dont know about the XRR, but im telling you right here that the FZR is the last car you want to get sideways.