Vauxhall Insignia autobox not changing down on slight incline

I have an intermittent problem where i'm travelling at any speed between 40 and 80 and in top gear then hit a slight incline and the car gives the feeling it auto changes down to a lower gear, the rev counter jumps up a little as would usually when gear changes but gearbox doesnt change, and as the car is loosing power/ slowing down it tries to change down again but still now physical gear change thus loses more speed. I then intervene and manually drop the gears down and up and then the car responds and drives normally. i have since this started 3 days ago have heard a noise that sounds like slipping clutch plate rubbing sound that you would get on a manual car if clutch was worn, and this noise happens just before when the autobox cant change down automatically.
Diagnostics say gearbox is fine but it could be the Torque converter at fault !
Any suggestions or directions would be most appreciated.

Many thanks for your time in advance