Hey guys bit of an odd problem. Kinda tough. My 4x4 won't engage. It was working great so I took it out and then it stopped working. All the vacuum system is good. Actuator works. Shift fork is working too. It's like the hubs aren't engaging inside the diff? I drained the fluid and I think i had water in there for awhile. It was very thin and dirty. I have to drive backwards for a bit to get it to engage and when it does it feels like it is binding in the front axle. It won't move at idle. Have to take it up to 1k rpm to make it move on flat level asphalt. Any help or pointers. I couldn't find any other posts about it. Thanks!

1999 f150 single cab,long bed, 4.6L.