Actually, after someone claimed there was a GT5 trailer shown at E305, I did some snooping around and here is the actual trailer shown there:
It was named Vision Gran Turismo, at it was a tech demo showcasing the view of PD for the next GT in the PS3, much like the vision S-E had for a next gen FF when they showed the FF7 tech demo. Notice how vision GT basically uses the GT4 engine with a few touch up, much like GT HD showcased when the PS3 released.
Never was it shown as a full game until the last E3 and never did it have a release date until last TGS. If you can find me a link proving otherwise then i'll be glad to say that I was wrong, but until then, it's all just speculation about old tech demos released by PD.
Current PC Build
CPU - i7 8700K 3.7 GHz (4.7 GHz turbo) 6 cores OC'd to 5.2 GHz with Watercooling (Hydro Series H110i) | MB - Gigabyte Z370 HD3P ATX | Gigabyte GTX 1080ti Gaming OC BLACK 11G (1657 MHz Boost Core / 11010 MHz Memory) | RAM - Corsair DIMM 32GB DDR4, 2400 MHz | PSU - Corsair CX650M (80+ Bronze) 650W | Audio - Asus Essence STX II 7.1 | Monitor - Samsung U28E590D 4K UHD, Freesync, 1 ms, 60 Hz, 28"
