As previously stated, negative "pop" is a possible problem which will be corrected by using glass carriers. Have you tried stopping down to the maximum to compare prints? A smaller diaphragm (exception being a point source head) should minimize focus (sharpness) problems stated.
Personally, (dangerous territory, I know) I found my enlarging problems dissipated greatly when I first invested in a "good" lens to replace the "entry-level, hobbyist quality" ones which came standard on my first enlarger - including overall sharpness. BTW, if you are doing b&w, the super modern, highly corrected $$$ lenses are not really required.