How to achieve advertised speeds?

I pay for 150Mbps down but only get around 130 which i am not complaining but i want it all
i have access to both the modem they provided me which is an older arris and a surfboard sb6121 which should be able to handle the speeds i am paying for and on my router i am using a custom Pfsense box i built earlier this year with a quad core atom with full gigabit ports so no bottleneck there.
My main question is where is the bottleneck that is preventing me from having my full speeds?

yeah hops between like 135 and 136

This ^^^^^^^^

Most ISP's say you will get "UP TO XXXMbps" which gives them a loop hole, I happen to live in a over sold neighborhood with shared infrastructure (Time Warner / WOW) (they share the fiber and some nodes have both of their switch/interface gear in them) best I can get with my own modem and a pfsense box during peek times is 100Mbps even though I'm promised up to 150Mbps, the way I can tell is the available bandwidth changes by time of day at dinner time it's 80-100 Mbps but after midnight till about 8-9am it tops out above the 150Mbps. (160Mbps-ish)

Of course if your using their modem they always have the ability to throttle you at any given time they choose, they say they don't or can't but we all know that isn't the truth.

Bummer man. I'm running an Asus RT-16N with DD-WRT and get my full speed all the time, or better.
I pay for 100/10Mbps

yea I would check your pfsense box. Maybe it's a weak duo core that's CPU capped at 100% when you're benchmarking.

No its a quad core and when i test it only 16% usage of cpu

All you can really do is call your ISP and complain.

In my experience, I've called and ran a speed test in the middle of the convo that gets it back up to speed. They are all shill.

i don't do a little better each time :D