I downloaded this app called "network spoofer" (My phone is rooted, Still have standard ROM on there) so I can troll on my friends network and replace all of the images with trollfaces on websites or redirect youtube videos to a rickroll video, After messing around with it I noticed my phone was running really slow and HTC Sense kept on crashing, So, With that being only app I downloaded I decided to uninstall it (maybe I did not do full wipe of it?) and I did google search on fixing the HTC Sense problem I had after searching I found what appeared to be a solution once I followed the steps the screen swiping was smooth again but after a while it started to freeze and HTC sense crashed again!
If what Vel said doesn't work, try to use a Task Killer seeing as the HTC's are constantly using the internet and apps. This being said, using the task killer temporary stops the apps you aren't using from being used. This should help with the crashing.
It could also be the battery overheating. Yes, it is possible. Just shut the phone down for a good 2-5 mins, and start it back up again.