Changing the ring and pinion gear set is a really major operation that requires special tools and the knowledge to set the bearing preload and backlash properly. They need to be adjusted very carefully to obtain the proper tooth contact pattern to prevent noise. It is not something most mechanics are competent to handle, and definitely it is not a do-it-yourself project. Also, remember that if you have four-wheel-drive, the ratios in both axles has to be the same.
Axle and spider gears can be replaced quite easily without touching the precision ring and pinion gears. I don't know what you mean by "went out", but those gears rarely fail or cause a problem. It's much more common, although still rare, for the large shaft going though the gears to pound the holes in the carrier oblong. That will cause a loud clunk when shifting between drive and reverse, and the truck will roll much more than normal when you put it in park.