You will need new carriers I believe the case break is 3.73 and down and 3.96 and up.
Carriers are only about 40$ though.
I would get tires first then gears. I currently have 3.55's and 35's. It is noticable ( i dont have 5th gear), but its a lot more economical going 65 in 4th gear at 2500rpm then 65 in 5th gear at 4000 rpm (getting gears first).
Just my .02