I just changed mine last weekend. I am an unabashed Amsoil synthetic fan, however, I depart from this when it comes to my tranny. I use Chevron Dextron (<99 cents at Costco) and Lube Gard additive (NAPA $13). Chevron makes some of the the best lubricants in the industry. And as far as the additive goes, it is the only one I use, period. Everything else on the market is a bunch of garbage (oil additives, transmission additives, gear oil additives, etc.). Lube Gard is OEM recommended, and more importantly, they come highly recommended by B&M Custom Transmission (Fresno, CA), a nationally recognized racing and custom transmission shop. With my six-cylinder Jeep Grand Cherokee, I tow a 4,800 lb. boat all summer long. At the end of each summer, I flush the tranny. Even with all of the towing I do (not to mention all of the other driving year round), the fluid comes out looking new. This was not the case before using the Lube Gard.