I'd personally skip Flat Pass if I could do it again... way too much dust and sand. Also last week was jeep week so the trails got hammered. Its been about 3 years since the last time i was at Moab and I never remembered seeing so many ATVs and motorbikes. Every single ride hand some kind of motorist on it. And Slick Rock is nice if you've never done it before. But if you skip it, its no big deal. Porcupine Rim is a must do everytime I go though.