Try using shadow focus, you can CS>Hemo>mutilate>5/6 rupture>vendetta>garrote>mfd>6p kidney(internal Bleeding)>ex
That will drop anyone without a immunity cooldown pretty much, if you don't have vendetta up you just pool or miss out garrote.
Garrote is much much lower priority in pve since it costs so much energy, it is always better to mutilate for combo points since if you have rupture up already you can put up creeping venom with envenom, which due to movement is pretty much a indefinite dot and ends up doing way more damage than garrote. Even doing a 3cp envenom is worth it as creeping venom does the same damage regardless of how many cp used.
There is argument of going subterfuge for the extra garrote damage thus giving it higher priority in your opener but you will run into the same energy starving problems, especially if you double cheap in the opener.
I personally prefer SF as it allows me to get my dots up faster due to having more energy and my opponents have less time to counter, but each to their own. The spec is much slower and requires pooling to be most effective, which goes hand in hand with gravitating to heavy pressure dot comps like RLS.