Got them from bestbuy, theres nothing printed on them, just your standard bestbuy insignia brand. All 3 CAT6s worked fine with my other pc, which is also hooked up to the same modem/router. 10mb upload.Where did you get the Cat6 cables?
What is printed along the length of those Cat6 cables?
Are you able to try those Cat6 cables in some other network environment?
Determine if the problem follows the cables or remains with the original network environment.