I ran into this issue again today so I thought I would share. I had a client who was experiencing very slow performance from his Remote Desktop Client to several servers he was accessing via TS Gateway. The problem turned out to be related to a feature found in Remote Desktop Connection 6.0 and higher. RDC 6.0 leverages the Receive Window Auto-Tuning feature found in Windows Vista and Windows 7. The problem is that the Receive Window advertised is much larger than it was in Windows XP which allows more data to be sent in larger, faster bursts. This is fine in a LAN environment but, when coming in via a WAN connection and then encapsulating the RDP traffic into an SSL stream, the net result was a lot of packet fragmentation. The following command will set the Receive Window to a more conservative value and consequently improve overall Remote Desktop performance.
netsh interface tcp set global autotuninglevel=highlyrestricted
Here’s the link to the original article that explains the problem in greater detail. Thanks guys!