I have gone back to using the keyboard with this unit since I have been having throttle issues with it on Rail Driver. The Rail Driver is calibrated and I have no issues with the F7 but with the SD-40 movement of the throttle on the RD will result in 2 notch jumps on the locomotive. Like N - 2 - 4 -5, you can't get back to notch 1 from 2, it goes back into N. Once you hit notch 5 reduction results in it going to 3 then 1 then N. Above notch 5 it seems to work ok. Also today I was running Fremont ascending and while blowing for the second road crossing the horn just stopper working. When I press the space bar or the button on the locomotive console it will give me "horn pressed" on the screen but no sound, bell works.
I have had a similar issue with the raildriver not only with Clinchfield but other routes as well. My raildriver is calibrated as well but the throttle does not seem to line up properly. I to have also gone back to using the keyboard for now.
I'm not having any problems with the throttle myself. Have y'all tried recalibrating? As far as the "disappearing horn" is concerned, this is a problem that affects locos on all the American routes and goes back many months if not years. It's not the only horn problem. There is no fix on the horizon at the moment, though some workarounds appear on the forum from time to time. A search might bring something up.
I've had this on one German loco but not on American locos. They all seem to work fine. I do get a bit of drift occasionally where it'll move from one notch to another by itself without me touching anything. Sorry to hear you're having issues. One thought, do you have RD plugged directly into a port on your PC or is it going into a hub? Paul