Are upload speeds throttled when using APIs with the hosts? I am assuming that is how TC interacts with them. I have a 1GB up and down fiber connection but uploads through TC never go faster than 3MB/sec. If I upload a file directly via their website, the speed is around 20MB/sec and if I use FTP for the hosts that allow it like Rapidgator, I get 50MB/sec per file with two files simultaneously. If it is an API limitation, do you have any plans to implement an option to upload via FTP for the hosts that provide it? Or, maybe a way to point TC at a file already on a webhost to create the post content with? The slow uploads are killing me and I have the upload limit set to 0 in the settings.

Another thing about uploads... Why is there only one running at a time? I have a file that should be going to three hosts in a post and it is uploading one host at a time, post by post. Why not have the option to upload to all hosts simultaneously with each post?

This heavily depends on file host. For example RG will always let you upload one file at the time while other hosts allow many more.
I usually set 5-6 uploads at the time cause server does not have really that good cpu and packing, making screenshots and uploading so many files is taxing on all resources which can decrease your upload speed.
I also have 1GB connection and RG always uploads full speed from what I can see while other hosts are half of that or less, but I bypass it as I wrote with uploading multiple files at the time so for example i upload 5 files at the same time to clicknupload and sum speed exceeds the limit I had while trying a browser upload.

Select more files / folders and you will see it's being uploaded to multiple hosts at once.

For one post - it's queued at the moment to maintain correct links order.

In "Settings" -> "General" -> increase "Processes limit" to process more posts / files at the same time.

In "Settings" -> "General" -> increase "Buffer size" if your Internet connection is better.

For FTP upload. It's literally not possible to get any link after FTP upload. FTP does not return any links. It's not possible.

For Rapidgator in "HOSTS" -> "Files" -> select rapidgator.net -> enable to "Use WEB upload" -> press "Update" button. After that you can increase "Requests limit at a time" -> press "Update" button.

can you please share screen short

Here is the screenshot: