Today I was pulling a small trailer and backing up felt a thump like I hit something when I put in in 4lo (snow today) now when I go the transmission slips and then seems to go into neutral and I cant go forward or reverse. I have to shut off the engine and wait a minute or two and then start it back up and go again. then it does the same thing and I have to keep waiting restarting going a little shutting it back off waiting again on and on help?