As with the update to 3.5.1 in the preview Channel, updating to 3.5.5 stable made this bug came back. GPU is oscillating between 200 and 1040 MHz, creating stutters and framedrops in game. Setting GPU to manual mitigate the issue, but this Is very annoying for a stable update. Just making a post to gather all of us and maybe get some attention from Valve.
Try capping your cpu frequency at 2800mhz with powertools (or just disable cpu auto boost)