Yes, different gearing in front and rear axles will not work. If you make the swap you will have to regear the front axle. 4.56's are not a good idea if you drive the freeway at all. I have 4.88's with 36's and still have a shortage of top end speed. Also, vibes will increase if go to that gear. The 3.73's are ideal for your set up. However, if you want more power and a big change, go for it.
Also, on the interstate, you will feel like you are giving it all its got to run 70 and that will def hurt your gas mileage.
1998 TJ Sport, 4.0 I6, 4.88's, super 35, Auburn lockers f/r, 7" RK, 36 Iroks, 15X10 ProComp series 51, K&N, swaybar disconnects, Ramsey 8500lb winch