I'm seeing that my upload speed (90M) is way under both what is advertised, and what other speed tests show. Is there a good way to test what my actual upload speed is?
The number that your ISP gives you is likely what they provision for your connection between you and your ISP
The number that a speed test gives you is the measured bandwidth between you and the server on the other end. This is expected to be different for different routes across the internet.
If you want to test just the pipe between you and your ISP, many ISPs provide their own speed test servers for this purpose.
examples:
I have fios 1Gb service. From clouldflare I see ~500Mb/s down and 90Mb/s up, and fast.com shows 600Mb/s down and 900Mb/s up.
It only shows a download test for me...
Yes, use iperf or netperf instead.