I image at 1058mm, so almost the same FL.
Use bin 2x2 and at least 10 seconds of exposure. 3 seconds is simply not enough.
Min star size 3.
About focuser, you have to measure it your self again for 10 seconds of exposure.
With moonlite i have 7 data points with step size of 153.
Try to cool down the camera to -10 if you can.
Strong wind and bad seeing can also quickly ruin the autofocus.