Also, it could well be that a JACK is not wired correctly. (This is common with wired Ethernet jacks that are installed by those familiar with telco - not LAN - wiring specs.)
RJ-11 (telco), unlike RJ-45 LAN, uses dual twisted-pair, not quad twisted-pair. Where the two crossover is RJ-11/45 xSDN/xDSL - note that both RJ-11 and RJ-45 cabling and plugs can be used for either. (RJ-11 is, in fact, used for voice-only hardware plugged into xDSL/xSDN, while RJ-45 is used for data equipment, such xDSL/xSDN "modems".) There is one RJ-45 jack that I strongly suspect of being incorrectly wired - however, I would need to be able to test the questionable jack in isolation, due to its location.
Why I suspect the jack: both ends of the connection otherwise (router and adapter) support gigabit Ethernet; however, the connection itself between them (wired) is only 100 mbps. The cables themselves (outside of the jack) are gigabit CAT5e, which leaves the jack itself as suspect.
If the jack is miswired, I CAN pull the jack and rewire it myself - all I need is time. (There is enough slack in the run itself that I won't need more cable - I can buy a new jack from RadioShack or MicroCenter. The jack is NOT integrated into the baseplate.)
Unless you are talking about rewiring the PCB traces that lead into an internal NIC card jack/router jack, there are no ethernet jacks in this house.