It sounds like bankupdatefrequency is not 4000 or not working right.
4000 times per second is every .00025 seconds (250 microseconds) so if you turn it on for 250 us, 4000 times a second it should be always on.
If you must use 32000us that would work with bankupdatefrequency of 31.25
The standard servo update frequency is 50Hz. It sounds like that is your real bankupdatefrequency?
I would probably use 20000us instead of 32000us so you don't get to full throttle at a little over half stick.