Moving the UCS from world (car position) to a particular plane

Hello,

I am fairly new to Draftsight.  But have used AutoCad / Mechanical desktop.  I see a lot of the same commands work and they are similar.  However, I have  a model, that is in car position.  I need to move the origin and level to different planes, and when I attempt to change the UCS, even identifying either of the axis....it doesn't move true to the part.  What am I missing?  In AutoCad, you can change to a 3 pt UCS location and pick the points on a flat surface, and it worked flawlessly.  That doesn't work on here. 

Thanks in advance.

A.Gore