Some applications slow on network (win 8.1), where to start?

Question

I recently got a new computer with windows 8.1.

I identified at least two applications are very slow when the are using the network. This is the MS dynamics AX client (very slow all the time) and RDTabs (a RDP client program which is slow when connecting to others servers).

But this does not affect all programs so I wonder if there is some kind of "classificiation" of network access of applications?

Example: Connecting to server1 with RDTabs is slow, using build-in mstsc.exe makes it run as it used to be. Also browsers and explorer work well too.

Where can I start to find the problem?