Question : make a gigabit rj45 loopback plug

I am trying to do some testing through different parts of a circuit connected to a cisco router. I need to make a loopback plug to do a hard loop.

I have created one loopback plug with the following pin layout:

Pin1 shorts to Pin3
Pin2 shorts to Pin6
Pin4 shorts to Pin7
Pin5 shorts to Pin8

If I put the cisco interface speed to 100 my interface links up. If I set the interface to 1000 the interface shows down/down. I tried this on a router interface and a switch interface with the same results. Can anyone verify if I have this pin layout set correctly for a gigabit loopback plug?

Thanks

Answer : make a gigabit rj45 loopback plug

Two possibilities that come to mind.
Some Gig ports (older gear) actually send and receive signal across all eight wires (500 MB per two pair).
With gig speeds, the cable and jack performance can be affected by the smallest of things.  If you used standard wire to create a home-made loopback plug, it is very possible you are creating near-end cross talk that is killing the signal.  Things like cable quality, jack quality, twist-rate of the cable, all are critical at high speeds.  Thus, what works at 100 MB may not work at 1000 MB.  Might be best to get a commercial product.