Extruded 3d text is set to glue to a surface while actually being slightly above the face to help avoid z-fighting. (when two faces try to occupy the same point in 3d space). This stops it easily intersecting with the face it is glued to.
It helps to set a negative value for the text so that it is already buried in the face, then unglue and pull,move or scale up just make a clean intersection.
If you just want the outline of the letters, use intersect with model and delete the lettering.
If you want cut in letters, set the correct negative depth, explode and intersect, then clean up.
