In the meantime, you said you didn't install any new apps, but on either version did/do you have any custom apps or drivers running? (Thing you saved under "Apps Code" or "Drivers Code" and then installed later.) If so, one of the first things you'll probably be asked to do is try disabling them to see if it helps.
If not, carry on. Just thought I'd mention this in case that is applicable and something you can do before they get back to you. 
