Philips 8631 Read/Write Speed Issue

I have both a regular DVD-ROM drive and a Philips DVD+-RW DVD8631 burner installed in my Dimension 4700, and they were both working fine for the first 8 months or so.  Then, I noticed that my DVD-ROM started reading at 1x max (1.81 according to Nero CDSpeed).  Since my burner was still reading/writing correctly, I didn't worry about it too much.  But, after a couple of weeks, my burner dropped down to the same slow speed.  I found the firmware update on the Dell site (GD30.exe) and flashed the drive, and the speed went back to normal.  Then my computer crashed, and I had to reformat my hard-drive.  Afterwards, both DVD drives worked fine for about a week.  Then, my Philips burner dropped back down to the low read/write speeds.  I tried telephone support, and they couldn't come up with anything.  I re-flashed the drive, and it didn't fix it.  Any thoughts on what the problem could be?  I thought maybe a conflict, but wouldn't that cause one of the drives to not work at all?