An oldish thread, I know - but since the last update (or so it seems), I've been noticing this happen to me a couple of times a day too.
The power-fade seems to come as I exit corners - the engine almost dies flat on me and even dropping a few gears does nothing much - it's like the car is getting indigestion...most odd.
An example is the Calsonic GT-R Super GT on the Nürburgring GT track after the Dunlop-Kehre corner. I'm on track, not overcooking it and then it just...dies. It didn't recover until after the Schumacher-S so I lost a good few seconds there.
I also had my Scuderia die out in a similar fashion on the Nürburgring proper - right before the finish line. Both of these cars haven't had an engine tuning in a while though, so maybe that's it.
Any more suggestions?