This seems to implicate the switch... are you sure that it is a 1Gbps switch and that all ports are functioning properly?
There should be no problem getting an iPerf test to work at gigabit speeds (i.e. ~940Mbps TCP) through any properly functioning switch (and cables) -- it should be transparent.
Sometimes cables can go bad... clearly okay in this case, but don't make the assumption that the cables are good without testing them to verify (and basic testers can be misleading here -- you need a pro-grade test system that can actually certify cables to know for sure)... it will cost you a ton of time and frustration if you happen to have a cable that has failed for whatever reason. Also, terminations and patch panels and couplers can cause issues. Just recently, I replaced a switch and it wouldn't negotiate with the upstream switch, despite what seemed to be a good structured cable (it worked at 1G speeds with the previous switch and tested okay with my standard cable tester)... turns out, it was a bad termination. I've also have had cat6 couplers go bad and drop things to 100Mbps.
Also, some switches and devices are more sensitive to cable/termination issues than others. Your trendnet could be okay for other runs, but unhappy with that particualr structured cable run.
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Thanks! 