i got my gearbox built 2 months ago and just started giving it a bit now though what i have realised is that when i am cruising in say second gear at around 40km/h and then flat stick it the car drops to first which is normal for kick down but the car revs out till 6500rpm and the computer aint tuned for those revs so it cuts out though the problem is why doesnt the car change gear at around 5500 rpm where its ment to be at could it be the kickdown switch on the gearbox or something wrong with my shift kit not allowing to shift at normal revs? when its cutting out though and i back off the accelerator the car goes to second and continues to go hard any ideas help appreciated thanks

take it back, its a fault / set up problem for sure.

when jatco's get rebuilt/strengthened/modified etc , they modify the valve body to give a firmer shift , but also it drags out the change , meaning it will rev out further than before. take it back and tell them , they can "fine tune" so to speak , to an extent.