First off, do you have a swing-timer? If not, get one -- it's a huge boost to Slam-usage.
The key to using Slam is to use it as soon as possible after a white attack hits -- and only once, unless you are swimming in rage (but then that's the situations I'd be 'saving' Mortal Strike for; it's expensive and rage-gain as Arms/Fury isn't the best). Spamming Slam will only result in you going rage-starved. You need those white hits.
White hit, Slam, Mortal Strike as Rage allows, Whirlwind as Rage allows, white hit, Slam, etc.