Yea I think it may be the speedo cable, I swapped the rear end to JDM discs (not sure if its zenki or kouki) and the gearbox is also a jdm box. The cable that was put in was shagged, so I swapped it with my adm cable...but I still had the same problem.

I am running 15 x 195 x 50 tyres so I know that would be a factor aswell.

I did hear there is 2 more teeth on a JDM speedo cable than a ADM one???? Not sure if anyone can clarify