No gigabit connection over a cat6 cable. RMA it or is it me?

I am in the process of upgrading my home network to gigabit Ethernet, and I have run into a problem. I bought two Link Depot C6M-100-WHB 100 ft. Cat 6 White Network Cables which I planned on using to connect two computers to a gigabit switch. For whatever reason they will only connect at 100 Mbps. I have checked the router and computers using a 20 footer I had laying around, and both computers and the router connect at 1 Gbps, no problem. I can only figure that there must be something up with the cable. I checked the reviews, and I don't see that anyone else had this problem. The cable either works or it doesn't.

The other thing I noticed (in case it matters) is that when I first tested the cable, I could only connect at 10 Mbps. The cable, however, was still neatly coiled from the packaging. Upon uncoiling it, it connected at 100 Mbps. I initially wrote off the 10 Mbps speed as caused by inductance in the coil, but with the uncoiled cable still not giving me full speed, perhaps the lower initial speed is a symptom of another problem.

I can only assume it is the cable, but I had always figured the cable will either work or it won't. Plus if there is a manufacturing defect with one, the odds of getting two bad cables are slim. So, am I missing something?

Thanks.