I have a 2003 Nissan Frontier EX 4x4 6 cylinder. w/ 123k miles on it. I just changed the tranny fluid about 1,000 miles ago(pain in the butt). anyway the problem i'm having is when I drive at between 40 and 45 MPH and I take my foot off the accelerator the truck acts like I put the breaks on. If i touch the gas at all it jumps into gear ( i suppose to a lower gear). When it does this it feels like the tranny is going to fall out. There is a big thud like it didn't shift right. but then everything is fine until i get back up to 40-45MPH and do it again. When i turn OD off it doesn't do this. sometimes it jerks into second gear but only if i step on it a little, like pulling out of the driveway fast. is my tranny going to fall out? what do i need to do?