What type oil goes in 1986 B2000 5 speed transmission?

I use 75w90 gear oil or 80w90 works fine on the weight.I would stick with standard gear oil and not use synthetic if it has alot of miles more than 100,000.Brand wise valvoline is fine,or coastal sold at advance auto or auto zone do great.Stay away from the valvoline durablend it does not do well with higher mileage transmissions or rear end axles.I change my transmission and rear end oil about yearly due to age of the truck and helps on the cold/hot temperature change.My recommend after 23 years of ownership of mine.