Hey all. I'm Gaz from the UK (born inPakistan). I stumbled across this forum when looking at GTRs. Nice to see Pakistan has a thriving tuning scene and some amazing examples of cars here.
To try and answer your question: the difference between a normal Skyline, GT-T and a GTR is quite big. Take the R34 Skyline for example. The R34 Skyline GT-T is a single turbo and rear wheel drive whereas the GTR is four wheel drive and twin turbo'd (RB26DETT). There are numerous other differences such as improvements to chassis, gear boxes etc.