I replaced an FP45 with an SD75 and I did manage to get up the hill at a minimum speed of about 14mph, though with sanders most of the way.
I considered presenting it as a download but lost it after MSTS became corrupted, I was forced to do a clean install, and I found that my 3DTS Tehachapi disk had quietly turned into a frisbee while it was sat on the bed. So I have now bought the download version and backed it up onto a reasonable quality disk.