First & foremost congratulations on loosing over 100lbs, that alone is a great accomplishment.
One of the reasons that the wight loss has slowed down is simply that you are probably much fitter now than you were when you started and your body has become much more efficient -it simply takes fewer calories to accomplish the same amount of work. (BTW - you're riding faster than I do on my 19km commute!) You're experiencing something known as exercise adaptation. (Lots of interesting reading if you google it)
Are you actually taking the weekends as rest days or are you doing some other fitness activity? Rest days are just as important as hard workout days. As long as you're getting your rest days there's no reason to go anything less than 100% (unless you're feeling fatigued) but you may want to add other fitness activities (walking, running, swimming, strength training) into the mix and then alternate easy & hard days on the bike (eg weights & easy bike one day, hard biking alone the next) and even consider building some interval training into your rides.
Good luck!