Red flashing orange light on burner

i did a firmware up grade to 2 sony dw-u18a they work great on 4x-r ridata with excellent playback ability. on 8x-r ridata however major, problems the red light flashes orange the speed drops and the dvd will not play at least wont play well. its like this it starts at 4x drops to 2x goes to 6x drops to 2x then goes to 8x resulting in a dvd that freezes and stutters. what can i do to solve this problem?