I believe the setting you really want is "Tonal", which is found by left clicking your sample which brings up the "Channel Settings". Half way down you should see "Time Stretching". The default is "Resample" but if you left click, a drop down menu will appear with different methods of time stretching but the one you want is "Tonal" (Maintains original tone throughout stretching).

FLS being as small as it is, I"m suprised it can handle this better than any other program I've tried.