I have a 2007 International 4300 with an Allison AT. I believe it's a 2000 series. I got done with my day after about 125 miles and I parked the truck to take a break and when I returned, the truck slammed really hard when into reverse and also into Drive. Drive felt like it wasn't in first gear....maybe 2nd or 3rd. Then after moving it about 200 feet, it felt like Drive was in neutral.....no movement at all. Reverse still works, but a hard slam when you put it into Reverse. Fluid was a little low earlier that morning, so I added a couple of quarts. Any ideas?