Nec ND 6500a not recording media at rated speeds

I have this drive in my laptop and it seems to start burning ok at rated speed of current media 8x. After about 1 minute the speed drops to 2x at stays that way until the end of the burn.

I have changed the firmware to a modded one and this is making no difference. I have read that Nec drives tend to air on the the side of caution when burning so drop media to what it thinks is best.

Anyone have any idea's?