Slumps often result from getting lost in the day-to-day routines and problem solving. Thus, some of the things I have found effective for coming out of a slump are things that make you look at your SO and vice versa with the fresh eyes of a new relationship. Those are probably personal, but some that work for us are:
Getting together in a group with good friends. I always admire my husband’s intelligence, wit and sweetness anew when I see him “on” with others outside the relationship. A secondary benefit is if there are some obnoxious folks in the group or crowd, I am always happy to being going home with my guy instead.
Road trip is one of our favorites. I think, though, that it should be any activity you two like, perhaps something you did a lot when you were first dating, but has tapered off. Maybe that’s dancing, clubbing, music, whatever.
Finally, I also endorse change of venue as others have mentioned.
Hope it goes well!