Update to the latest version which was compiled against the latest SDK. Once done, go to where it is installed and open up the FSUIPC.ini file.
At the end add
NumberOfPumps=0
Save and test.
This was identified as an issue during SU11 I believe it was, the message is spamming non stop. Adding NumberOfPumps=0 stops it and the stuttering goes away (if this is the cause).
Also they updated it for the latest SDK available.