I have a 2005 F150 Lariat. It has 121,000 miles on it. I've had it for the last 8 years. Recently, I've had problems with it shifting into reverse. The problem is only when I shift from Drive to Reverse it wont engage Reverse all the time. If I shift from Drive to Park and then back to Reverse it will engage. I did recently have a transmission fluid leak. I replaced a transmission line and the cooler. The fluid was a little low, but that was for a few miles and not low enough that it was below the line on the dip stick. However, the problem was occurring before this. I also now have the U1900 Code. I am not sure if that has anything to do with it. Any suggestion would be appreciated! Thanks in Advance.