Hi,

I am not sure why there would be a pause at 1000 files, there is noting in WatchDirectory doing this so I must assume it is something on the server side (FTP).

About the upload speed, you are correct WD uses a single upload thread. Currently there is not much you can do about it.
One thing we found out.... Some modems (firewalls?) give preference (speed!) to certain known file types (for example *.mp4 files) and lower the speed of other file types. "Quality of Service" is a typical name used for this setting. If you use the option "upload files with a .partial extension, rename when complete" it will always be an unknown file type.....

To simulate multiple upload threads....
stop the task
right-click it and select "Copy" from the menu that pops up to create an identical task
Use the "Filter Events" settings on both tasks so these tasks work on different sets of files.
For example, task-1 only uploads files that have names starting with A, B, C or D
task-2 only uploads files having names that do NOT start with A, B, C or D (see attached picture for this one)
Obviously this will depend on the naming of your files so be creative.