I tried using my full-tune Evo VIII MR on Grand Canyon. It had worked just fine on Costa Di Amalfi and Umbria, so I figured it wouldn't be too different on dirt. Boy, was I wrong.
I ended up taking off the Stage 5 turbo, ECU, Exhaust, Original suspension, VCD(it was set at 20%), and the AYC controller(set at 80). The car was down to about 380hp, but it was great. I think my problem was having too much power. Not only did I take the Grand Canyon, the Ice Rally, and Chamonix after trying them again, but also both Yosimite rallies and Swiss Alps on my first attempt.
Oh, and I'm horrible at rally driving.