Yes, it is known that latest version of AVG may indeed cause slowdown issues on some systems. Good you already found it yourself and fixed it
Glad I could help.
Please read my Prevention page with lots of info and tips how to prevent this in the future.
And if you want to improve speed/system performance after malware removal, take a look here.
Extra note: Make sure your programs are up to date - because older versions may contain Security Leaks. To find out what programs need to be updated, please run the Secunia Software Inspector Scan.
Happy Surfing again!