Performance problems glDrawElements / glDrawArrays

With a Quadro 4000 under Windows 7 x64 Driver 320.49 there is a weird problem with the performance of glDrawArrays (and also glDrawElements). In every other Frame (2nd, 4th, 6th etc.) the execution time of glDrawArrays is 10x the time needed for the other frames. The problem is gone when running the program from a debugger. It seems not to be a heap problem as the program runs fine with _NO_DEBUG_HEAP=1. Does the driver check for a debugger and change behavior on that? Any other ideas what could be the problem? The program behaves as expected with other NVIDA cards (GTX 760 or GTX 285)