CANT burn at 48 x ? after flashing

Hi ive flashed my 40 x liteon drive with the vs06 firmware , but when using trax data’s and ritek unbranded 48x speed disks ( after using the liteon smartburn prog they are both the same disk but are 48x ) , every time it gets to just over 50 % and 35x and then drops down to 24x , ive used other progs and its the same, if i use 40x datasafe then it writes to 40x , and if i drop the speed to 40x instead of max it still drops to 24x , ive reflashed it back to original firmware and it writes to the end of disk at 40x ? really wierd ,

PS i used the reg edit hack so nero tells u exactly the speed its writing at and goes up and down etc like clone does