There must be a bottleneck or other issue, then. A 1Gb/s link really, really is always 1Gb/s on the wire - it's not physically possible for it to be anything else. Gigabit Ethernet isn't "up to" a gigabit, it's a gigabit or no connection at all.
The first thing I'd do is check that the link layer really has come up at 1 Gbit. If you're using a cable that's on the limit in terms of signal integrity (very long, poor quality, damaged or mis-wired), the PHY in your PC and/or connected device might fall back to 100BaseTx.
There's no guarantee that any particular device is able to keep up with the speed of the wire. Are you connected to a switch that has other devices also plugged in? Could there be a significant amount of other traffic that the switch's CPU has to cope with? Not all switches are "non-blocking", ie. traffic between one pair of ports doesn't affect traffic between others. Some switches, especially older ones, have an aggregate throughput limit which is less than (number of ports) * (max link speed per port).
If that's not it, then maybe the device you're ultimately talking to just isn't that fast, and the Ethernet link speed isn't the issue.
It could also be a protocol issue; a badly configured MTU somewhere can cause a great deal of packet fragmentation, retransmission and loss, all of which can cripple the useful throughput of the interface. A session with Wireshark could be time very well spent to see if this is happening on your network.