I've been playing a few matches since I created the topic, and I've realized synergy is extremely important in 3 Pokemon tier. You only have three slots, which makes it that much harder to cover most of the threats. Of course, you also have to focus slots on Pokemon that can sweep and blast through everything else.
One Pokemon I've found that is really effective is Heatran. Heatran has so many excellent resistances and thanks to the very fast paced nature of the tier, it can use Air Balloon really well. I've been using an offensive variant with Fire Blast / Hidden Power Ice / Earth Power / Substitute @ Air Balloon and it's pretty awesome. Fantastic check to so many Pokemon, especially Dragon-types. It's one of the only things that's discouraging me from using Venomoth. Sleep is so much better in 3 pokes tier because you can make 33% of the team useless. I'm sure Quiver Dance / Sleep Powder / Bug Buzz / Roost/Substitute Venomoth @ Tinted Lens is really good against teams lacking powerful and fast Choice Scarf Pokemon and Scizor and Heatran.