This four speed automatic was first used in 1982 and continued until mid 1984 as a first design. An improved sprag clutch was introduced in mid 1984 but it doesn't fit in the earlier transmission. This model is much more durable. If you don't feel confident taking the transmission apart, repairing it and resealing it, then replacing it with a used one is relatively simple. This transmission was used from 1982 to 1990 and was used in most GM rear wheel drive vehicles.
Some models require the transmission tail housing to be switched however.
Truck transmissions up to and including 1987 are a direct bolt in. Premium may be 'fuelish' Q . If your engine is designed for regular fuel, then using premium fuel is only wasting your money. The main advantage of premium fuel is its higher octane rating. High performance engines with high compression ratios need a fuel that does not self-ignite as easily.