I hope this isn't too basic but have you done all the usual cleanup things like getting rid of all temp files etc., that can pile up especially through IE use? have you checked free space, do you defrag occasionally etc? wondering if could be resource issue and not just virus or malware type thing

Lastly if IE in particular is slow, have you tried using a different connection to the internet? just as a comparison. Also support above advice about using chrome as lots faster than IE.