Problem with Volvo I-shift AT2612F

Hi
I have a problem with my I - shift transmission on volvo FM (4) M.Y 2018, the problem is too late downshifting, the RPM reaches 10000 rpm then the transmission downshifts, the truck lose power because of this late shifting,
in the past it was downshifting at 14000 rpm it was ok,
no diagnostic trouble code appears on Engine or transmission,
any ideas?
Regards

 

Yes i have, the problem exist with both E or P on the dashboard.
It works fine - shifting at higher rpm- only when i press B ( brake mode) in the engine brake control lever.
I need it to downshift always like that at higher rpm.
Thanks to your reply