When I received my XPS 14z a month ago, I bought a Crucial M4 128 GB SSD capable of SATA III connection and installed it into my laptop.  At first it does 6Gb/s, but after 5 days, it goes down to 3Gb/s, which is SATA II, and stay there.  I can confirmed it with Intel Rapid Storage Technology Application and many different SSD benchmarks.  I talked to Dell and because of an overheating issue along with this issue, they came and replaced my motherboard and CPU.  However, the problem still persists.  Dell said I might have a defective or incompatible SSD and that I needed to talk to the vendor or manufacturer.  I decided to return the Crucial SSD and bought a Samsung 830 128GB SSD instead, the same model and brand used by Dell on this laptop, only smaller in storage size.  The problem didn't go away with this new SSD.  Once in a while after a couple of days, it would have SATA III connection, but after an hour or two, it would go back to SATA II and stay there most of the time.  I don't know what is going on.  After doing research on the situation, I think it is more of a firmware or software issue on Dell's part and not a hardware issue.  Does anyone have a similar problem???  Also, if someone has this same laptop model that bought the 250GB SSD option, can you check to see if you have SATA II or SATA III connection???  Thank you.