It is my understanding that if money is tight, replacing just two tires at a time on a two wheel drive vehicle is fine. Heck we do this on our Police cars sometimes. But on All Wheel drive vehicles (no low range transfer case) and four wheel drive vehicles, (like yours) it is almost always advisable to replace all four tires at the same time.
258 cu. inch six, Team Rush ignition upgrade, T5, Dana 300, Superwinch lockouts, Black Diamond 3" suspension lift, greasable shackles, poly bushings, JKS quick discos, 32x11.50x15 Cooper STT's, American Racing 23 15x8 alloys, Uniden Pro 520XL CB radio, 2' adjustable tip Firestick antenna, Viair 460 onboard air system