this was my issue, however yours looks more severe mine was just like a singular spike that lasted a second or two whenever i entered some places. have u monitored ur cpu usage/temps while this happens?
i had this issue, and it was due to there being stuff left over from old/deleted addons in my garrysmod folder. you can clear them out or if ur lazy like me just do a fresh install of garrys mod by deleting the whole garrys mod folder