I just changed my transmission fluid for the first time. I have a c6 3 speed automatic. Napa said it calls for 12 quarts, I question this because they gave me the wrong filter/gaskit kit. I put in about 11 1/2 quarts and the dip stick reads way up the stick, but this could be excess fluid from pouring it in. Does any one know how much fluid to put in this trans? My gears slam in harder then normal. Its been at least 20,000 miles since the fluid has been changed. I purchased it that many miles ago and have been doing a lot of hauling. Also what kind of fluid. I used dercon 3 but I heard type F goes with the c6.