If I lift my YJ 4.5" do I need to modify my drive shaft and or steering linkage?

Yes well kinda,

All the research I've done says that if you have greater than a 2.5" lift you need to lower your transfercase

Most 4" kits come with the lowering spacers and bolts.

I havn't seen a 4.5" lift though.

If you have the money, I'd recommended going with a CV joint on the rear driveshaft, rather than lowering the transfer case. Whiile lowering the transfer case will reduce the U-joint angle on the rear shaft, that procedure has two disadvantages: (1) it actually increases u-joint angle on the front driveshaft, and (2) it reduces ground clearance, which was probably the point of the lift and bigger tires.

You will probably have to lengthen the driveshafts. To see if you have to, after installing the lift jack up the frame at both ends of the vehicle and put the frame on jackstands. The tires should not be touching the ground (i.e., at full droop). That will extend your drivehsafts the full amount. Having done that, measure and make sure you still have sufficient engagement of the splines on the slipjoints of the driveshafts.

Thanks for the info, this site is really helpfull. My reverse lights don't work either "98 Cherokee sport". I'm gonna try cleaning my "NSS". I wonder on the YJ I mean would this jeep require slip yoke eliminator or does it come stock w/out slip yoke. Wich is a cheaper and or easier build up.