Has the tranny been flushed before, if its a high mileage vehicle flushing the tranny for the first time can cause more harm than good. If so, drain the tranny fluid and change the filter, refill with new fluid. Drive it for a week and then drain the fluid again and refill. The stuff I have in my diffs right now is Amsoil Severe Gear 75W-90, the Redline tranny fluid that was mentioned is good, its going in after the 101.