If its just a flat surface, you could just use a facing or pocket toolpath in 2D? Don't need to use a surfacing toolpath.In this example I am simply trying to machine the top of a piece of stock to leave a flat surface.
As for the steps downs, it may be the way the stock is drawn, toolpath selection, containment selection, etc. Need a bit more info here (stock shape, Z offset, surface toolpath used, etc).
That actually may be coming from a setting in your toolpath parameters. Look on one of the tabs and click on "Cut Depths"... There's probably a ".2" value set in here on the Incremental tab. This will add (or subtract if negative) value to your cuts (at top and/or bottom)...Mastercam seems to ignore that too and automatically adds 0.2mm to everything