Claras, I would cut down on your exposure time to a couple of minutes and use stronger developer (around 3 minutes developing). Remember you are exposing for the shadow areas. It's opposite, so if you have no detail in the shadows, then you are exposing too long. The developer builds up your density (or your high-lights). So unless you have really dense original negs, two to three minutes exposure should be fine. This is also for printing an 8x10 size.