I have a 2000 Ford Explorer XLT with a 4.0 L SOHC with 4WD, 5R44/55E trans, all my forward gears shift , (up shift and down shifts smoothly automatically and manually smoothly) but I have no reverse, it sounds like it tries to move, I can hear and feel it try but it will not back up. Put it in any forward gear and it move no problem. Fluid is up to level, clean and has no burnt smell, this problem just happened, no warning, no slipping, it just stopped going in reverse, the shift lever moves smootly between gear, no cluncks, no whining, no grinding. I'm at a loss, been a mechanic for 30 years worked on cars, bikes and boats so I'm no stranger to rebuilding engines and transmissions but this one kinda has me stumpped, any help or directions for trouble shooting would be appreciated. Thanks in advance for your help, you folks have helped me before so I have faith that you'll be able to help me out again.