How hard is it to change the rear gear oil? What is needed and what should I replace it with. 1994 sierra 5.7 2wd

not hard at all man all you need for lube is 80/90 gear oil

If it is a Limited Slip diff. you will need a LS gear lube .

ls gear lube started in 99 had to check that out when i changed mine. chevy dealer said 99 and up