I have just simmed myself on Raidbots and AMR and have different gear suggestions, Raidbots sims me at 88k but with the best suggestion from AMR i get simmed for 85k, please could someone take a look and explain why this is?
AMR:
fc0074e50cee49fe9eba8596868311bf
Raidbots:
https://www.raidbots.com/simbot/report/nmUqRCmpbjG7D4Gk5v9vab
We base all of our gear recommendations on data generated from the AMR simulator. According to our simulator, the BiB suggestion will slightly increase your DPS.
SimC is a different simulator with its own model of the game. Raidbots runs simulations using SimC. Both models are good, but they aren’t exactly the same and neither model is created by blizzard - so neither model is exact. The DPS number you get in either will be slightly different.
The other main difference for beast mastery is that SimC assumes you will use your pet’s basic attack exactly on cooldown every time. To achieve this in-game, you have to macro the pet’s basic attack to every ability you’d use and spam buttons constantly - this is because of a long-standing behavior with pet auto cast abilities that introduces a slight delay even when the ability is ready. Some players know about this and play accordingly, but many (most?) do not, so we model it as if players are just using the built-in auto cast. It’s also really a pain to constantly spam buttons for this gain 
Thanks Swol for responding. Does the BiB feature suggest new neck essences or can we make it so that it does?
It can, based on the Essences you already know… the Class Guides give a recommendation on what the best ones are in the Talent picker section - if you look at the Essence lists you’ll see “within 5%/2.5% of optimal/best” noted at the left side, which indicates the effectiveness of any given Essence for the spec. guide you choose.
Use that for your Major essence choice & you can choose/create a build based off that Essence choice; I will add that the numbers are recommendations based off the data used for BiB/BiS, so you should use the recommendations and factor them into your own working knowledge of your character.
You didn’t include a link to the AMR sims you ran @swatto86, hopefully you chose ranged target dummy as that’s the closest match to what SimC uses.
In the sim result you listed I noticed Symbiotic Presence Uptime 90% which seems incredibly optimistic to me and I’m having trouble finding a log with a hunter using it.
I’ve got no idea why people keep using Patchwerk given nothing is like that fight any more, at least as a BM hunter you can probably treat Shad as almost like that, assuming you don’t need to turtle and can keep using your abilities while doing the movement.
BM loses almost no damage from movement, though, so it’s probably the spec where you’ll see the least deviation from a patchwerk sim for single target dps.
Almost but not everyone can do movement/mechanics like a simulator, although we’re comparing simulators here.
I haven’t looked at the ST script for a while, is it just movement within attack range?