Blame it on auto zone and part stores people assume they know what they talking about I just heard them tell someone to use gear oil and I got kicked for intervening the blame lies thereits like a retard convention in here. Gear oil is for rearend gears, i never saw a post with him saying he needed to change rearend gears. Mercron tranny fluid is what you need or GM syncromesh can be used also. Just drain the damn thing, pop off the shifter and pour directly into the tranny. About 3 quarts. pull the fill plug and stick your finger in there, after 3 quarts you should feel some fluid at your finger then you are good.