Will h

Hi guys need help!. Got a gs 450h 2008 model. Its started making a funny knocking sound (very quite but I know its not right). So, I decided to give it a good thrashing to see what happened, and when the car reached 80mph, the power cut out !!. So, I took my foot off the light speed pedal and put it back on and it was fine ?.

I tried it again and it does it nearly every time. It feels like its trying to select a gear, but i know the car doesn't have conventional gears. It is fine if i go from 50 - 80 or 60 - 80 but when i go from under around 30, 35 and floor it, the car losses power at 80mph every time !? 

It definitely feels like a transmission problem any help ?.

Oh. and the cruise control feels a little 'unsure' or jumpy ?

Please help, thanks.