You also might look at your negatives. If they are exposed at the same EI you use for silver printing, they could be way too dense. I found this out when I first started platinum printing. I was rating my tri-x at 200 (the same as I shoot for silver). I now rate it at 400 or higher, depending on the development. In effect, I was overexposing the negative and I had to print through the extra exposure with linger times under the UV box.