The driveshaft in GTS-Ts have been known to wear over time, especially with highly modified gts-ts
The most common problem is tailshaft backlash which can come in the form of noise/vibration from the rear in a different degrees.
When I had my recent service, my mechanic said that I have a bit of tailshaft backlash present - still can't pick it myself but its there none the less.
With this wear starting to happen with mine, and me only only making 235rwkw, I'd say it would be a good idea to upgrade the diff if your making 300rwkw +
GTR diff will be bullet proof. Get a recon'd second hand one and you'll be laughing.
James