2000 Ford Expedition When Shifted in to reverse. Truck wi

Hello, I pulled my truck in the garage the other evening. The next day I started it. Put it in reverse and it moved a little and acted like it was pushing a wall. It will go into forward gears no problem. I shifted it into neutral and tries to push it out. No luck (engine running and engine off). A week ago the ABS light came on.I unpluged the ABS sensor on the rear axle. No effect. I did notice the left rear splash shield had oil and dirt build up. I think the rear left seal is leaking. The rear disc brakes are fine, not binding, no leaks. I have not pulled the rotors yet. But I need a few ideas what this could be. This weekend I plan to take off the rear rotors and pull the left rear axle to see if the bearing is broken. I have had no harsh bearing noise or any noise at all leading up to this. Just the abs light. I was able to get the truck to back out of the garage about ten feet. A few clanking noises occurred, the truck engine was not over revving but straining to move in reverse. Forward is normal.I work for Ford and have access to the online workshop manuals. Any pointers would be greatly appreciated