When I used my HILTI drill motor on 3 roller mill the rollers did not spin in-sync. I took off the bottom most roller and was then able to get a proper spin. I operated the mill like that for a while, obtaining a good grain crush with only 2 rollers. However, I then reassembled the 3 rollers back on the mill and tried a 650 rpm motor on it and the rollers still were not spinning properly. It wasn't until someone on this forum informed me that the the rpm's needed to be much lower than 650rpm's, and lower in the range of around 170 rpm's.
I suspect this might be the same for your 3 roller mill. But I may be wrong, because I have the older model. Check the mill's website for your specific specs. Let me know what happens.
There's a couple of post on this forum that deal with the set-up and the motorization of the that type of mill. There are a couple different inexpensive, and straight forward ways you can use for motorizing your mill. If you can't find the info, let me know and I'll post my set-up.