there could be plenty of reasons. the most convenient one would be that you are fiddling with it more because of the JB!
Or it could be due to you having plenty of apps, processes running in the background?
You might wanna install "Remove Background" from Cydia. It's a tweak that lets you remove all the apps from the task switcher, and the apps processes killed too with just one touch.
Try and see if it works, and monitor from there again what you are running, frequency of use, etc.