I have recently done a full rebuild on the the 302 I have in the bronco. While the motor was out I decided to change the trans fluid and filter. Now it slips bad in the first gear and then after it slips a couple of times it shifts flawlessly. Now it only slips after its been sitting for a day or so. Its seems the more its driven the better it gets. I mean it slips at first then it shifts so smoothly. After about three shifts it gets pretty smooth and the more you drive it the better it gets. You can barely feel it when it shifts at its best. Its like it needs to get the fluid going in the gears and then its fine. I am thinking bad valve body seal. What do you guys think. Would a shift kit help because I can pick one up new on craigslist real cheap right now. Its made by B&M. The trans. did sit for about 2 to 3 years. Should I keep driving it and would it get better the more it gets driven? Is it because its been sitting for while? Here is the fluid I used. Could it be the fluid? http://www.valvoline.com/products/brands/maxlife/automatic-transmission-fluid/37 Now we bought it not running so we don't know if it was slipping prior to it been sitting. Thanks for any help!