I have nVidia gts450 (with 1Gb DDR3 and gf116 core) with default clock core/memory: 595/800. Upon alt+tabbing or exiting most games it goes from P0 to P8 (405/395). I've already set "prefer maximum performance" for all apps (using nvidia inspector profiles). I found 1 solution (but it didn't last long) - using nvidia powermizer manager I've disabled overheat shutdown and enabled fixed performance level at max. It's definitely not overheat problem, since I've ran FurMark for at least 15 minutes on overclocked 810/900 with 1,062V - temp goes up to 90 and stays there (max temp for gf116 is 100C). But for some reason gpu is still goes to P8 (even in default clocks) upon Alt+Tabbing out of game or exiting the game, not all time tho, but frequently.