A show like South Park will always have slumps in form considering how it's made. South Park is in desperate need for big news to happen for it to be at its best, even though those kind of episodes aren't always the best, but they are needed to complement the kids being kids episodes.
Saying it has jumped the shark would be very harsh. So far this run we've had two poor episodes (Dead Celebrities and Wrestling), one decent (Whale Whores) and one very good in Butters Bottom Bitch, and even the poor ones will give you a few good laughs.