You should try switching lead rain and bold of the storm with stim pack and nexus frenzy. Stim pack is just as good as an escape if your proactive and aware. You can also turn around and pot shot a pursuer or just keep running. You can also chase with it. Additionally having both nexus frenzy and stim pack is like an additional 3 second overkill, and when stim pack runs out you still have tychus's amazing DPS which is nothing to scoff at with the recent range buff.