I find with AC now that it can change in performance over 30 mins and i have to close it down and start again, or ever so often i clean out SOL and CSP and start again.
Hi Safi. Have a look at this post. You may well find your slowdowns are caused by the assettocorsa.exe getting logged as 'faulty' in Windows due to various bugs that have made it crash too often and added a flag that slow it down. So, if you add 'assettocorsa.exe' and 'Content Manager.exe' to the 'fault tolerant heap' exclusion list in the registry editor, things may well improve.
This youtube video shows how to add a program to the exclusion list. If you follow the steps shown and just add the AC and CSP apps to the exlusion list instead of the app that added in the video, that's all there is to it.