You've ventured into a complex subject, Andy. I'll go over a few points in order of complexity.
It may well be technique. When your skis start to slip it's natural to lean forward at the waist. Unfortunately this moves your weight even further forward, lessening the weight on the skis and thus their grip. Keep your spine upright, and bend at the knees when going uphill. Practice, practice. Do not look at your skis, a sure sign you're leaning forward.
Rossi fishscales are not the most aggressive out there. Alpina and Karhu skis have more aggressive patterns that will climb a little bit better.
Fishscales work best in dense, moist snow. Early season snow tends to be light and dry.
I use iron-in glide wax on the fishscale areas of my skis, because it stops sticky snow from icing up on the bottoms. This is only a problem in certain conditions. I iron the wax into the fishscales as usual, then pass over 10" areas with the iron on high heat, using paper towels to soak up the excess wax, then a razor blade to clean the final bits of excess wax out while it's still warm. This is a pain, but worth it, and doesn't have to be done too often. Spray on waxes are, IMO, worthless.
You might consider kick skins, rather than full length skins. In either case, you'll want skins the full width of the ski underfoot, with the metal edges just exposed.
Aside from kick waxing (which is very effective in light, dry snow), kicker skins might be your best option.