There's some talk in this thread about this being an overheating problem or Samsung artificially boosting the TV's capabilities. This seems to me like an algorithmic problem or software fault, not a mechanical problem or hardware fault.
The TV is using global dimming to artificially boost contrast, yes, but this makes sense and works well when the screen is totally black or near black. The problem is that global dimming is configured differently for Movie mode versus other modes. The dimming works reasonably well in Movie mode because it has a fairly high threshold for how dark the screen has to be in order to dim. It's totally broken in Game mode because the threshold is far too low. This threshold should be user configurable. That we are given easy access to white balance, which the average user should not touch, and not global dimming threshold seems very silly to me.
Now, the six minute thing could be a different issue. That could be a programmed delay for any dimming so as to warm up the display. (LCDs don't need to warm up like plasmas did, but will be sluggish until warmed up; calibrators generally leave LCDs running for 30–60 mins before calibrating, warming the liquid-crystal using the backlight, but most of the warming happens in the first ten mins.) After this delay, dimming becomes active and for Game mode, the low threshold means it's dimming all the ***** time. It could be that you can reset the algorithm (and restart that delay) by changing local dimming mode or some other settings, which is how you can temporarily stop it from dimming again.
If I'm right about how this is working, then the problem is the threshold. Global dimming should be user configurable, just like local dimming. Samsung ought to give us high, standard and low threshold configurations for dimming. If they won't do that, then at least set the threshold for all inputs to Movie mode levels, which seems unobtrusive.
