Sony Burners are inconsistant (Sony DRU-710A)

[qanda]This thread is about the Sony DRU-710A. Click here to see full specs[/qanda]Hello everyone. I am new here. Pardon me if this has already been addressed here however I could not find anything.

This refers to DVD burning.
These problems exist no matter what software I use.

I have both the DRU-710a and the DRU-835A installed. Firmware has been update for some time now and DMA is on for all drives.
For the longest time I was getting 16X on the 835 and 12X on the 710 with no problems at all. I have not changed media brands.

Here is are my problems:
On the 835, when I start the burn, it goes for a little while then stops burning, then it starts up again, then stops, then starts… this goes on until the burn is complete. The copy turns out however, instead of taking 5 minutes to burn a single layer DVD movie, it is taking 12 minutes.

Now for the 710:
I was getting 12X speed ever since I bought the drive and after updating the firmware. Now it will only burn at 8X. The burn continues until done, unlike the problem with the 835, however I can not get the full burn speed any longer. Again, same media (Verbatim).

I am running XP. I have tried unplugging the 710 and 835 one at a time.
I have uninstalled them and let window detect them again.

I am stuck and would very much appreciate if someone has an answer for me. Thank you all in advance. Looking forward to your replys.