Chevy & GMC Vans

Just got a cherry 98 awd I want to change and or add all fluids What brand( synthetic?) and weight diff fluid should I use? Is there an additive I should use? Thanx

Im looking for an opinion on this too.. Owners manual for 97 says 80w-90, but service manual for van says 75w-140 for posi rear end.

So what ones really right?

Scott

did a little more reading, the synthetic 75w-140 is going in.

75-90 gear oil is good for both front and rear diff's. If you have a posi, limited slip lube is needed unless you use most synthetics. They usually already have additives for limited slips. As far as brands, I use Amsoil most of the time.