I dont think a K&N filter the cheapest and best upgrade one can make. Im not trying to be an a$$ or anything or make you feel bad about your purchase, but your taking out a OEM air filter with superior filtration capabilities compared to the K&N and putting in one that will make no noticeable difference in performance, allow more debris to enter, the hassle of having to clean and re-oil (which also tends to get on intake sensors if over oiled), costs more money etc etc.
Im not saying using a K&N will destroy your motor because that would just be stupid to say, but I dont see any real benefits of using one especially in a Grand Cherokee. Im not saying I have never used a K&N or some sort of cold air kit, but that was in my Corvettes and stuff like that. In a Jeep, I will take the one that filters better any day :-) To answer everyones question no you will not notice any increase in performance with a K&N, and if you do its your mind playing games on you because you spent $45+ on it!
ok im done being a negative nancy sorry long day at work haha.