Excellent, already such result as 92 % for google speed and 78 % for yahoo , are okk , me i have 97 % FOR GOOGLE SPEED AND 87 % for yahoo !
you may notice on the parameters on GTMETRIX that they check too the compatibility or the optimization from the side of the code, java script and css , so those codes are related to your theme !!!
so now if you have made any update for wordpress or for your theme that can be the reason to slow your website , so you have to check with the default theme of wordpress.
i hope that can help you
cheers
