before we get this started, you have to figure your desired speed, with 128 being the fastest climbing speed and 99 being the slowest (lowest usable rate). I personally use 110. Keep in mind that the higher the speed, the serverhost's CPU will have higher utilization possibly causing FPS drops

If you're hosting a dedicated server (not p2p invite through steam) then put this into your console:

sv_tickrate = 110

OR if you are using P2P, which is basically everyone using this addon, put this in your console instead:

cl_updaterate 110
cl_cmdrate 110

this will save next time you close GMod so you only have to do this once, keep in mind that if your FPS is below this rate, the tick rate will be updated to match your FPS.

Higher Speed = more performance intensive and vice versa