My grass fed ribeye vs corn fed is always dry, tough and tasteless. There in little to no fat in them it seems. I gave up. Am I missing something? Does marinating help?
Grass fed has much less fat in it than standard corn-fed. Corn-fed is marbled with fat through and through. It responds very well to the traditional blast-sear, then finish-in-oven method discussed above. Do that to grass-fed, though, and you're going to blast it into shoe leather. Especially if it's not cut very thick.
If you want to stick to the traditional high-heat method (in a skillet or on the grill), then watching it carefully, eating it rare, and buttering it are all good ideas. A different, more reliable, way is to do it lower and slower, oven-roasting it at a steady temperature in the 200's. The Argentinians do it this way. It ends up cooked through, not that gorgeous red-pink-juicy look like in the Beef Producers' Assn ads, but it's tender and flavorful. Also responds well to sauce, like chimichurri.
I've only done it this way a couple of times so I don't feel confident enough to give you specific instructions, but google Argentinian grass-fed beef and you should find recipes for doing it this way.