I have followed your clear instructions and your links and my RailMaster is now v1.74 (5?). My existing loco's, well two of them, operate as always. There was no difficulty in the download and installation of v1.74.5. I manually added my new R3866, v5 decoder to the Roster, repeating what I had attempted in RM v1.73. I explicitly followed FAQ No 4 as recommended and entered all data by hand. The operation of the loco has not altered at all. The sounds are available, the speed curser shows the pink maximum 127 speed steps but any input of 1mph or greater sends the motor to a constant fast speed. I have repeated this manual loading with no change. Do I need to start looking at the decoder cv's for the loco motor? More advice needed.