Drivetrain Differential Issues?

Took the mustang out for a short drive today. I got on it a bit in second gear and shifted through 4th. Looked behind me and lots of whiteish smoke out the back and has a burning smell almost like clutch but not quite. The rear locked up for a couple seconds and now has a bad vibration I can hear and feel through the shifter. I was able to limp it home. Didn't see any leaks from the rear.

Is it possible I broke an axle or sheared off the splines? Not sure if I would still be able to move if that was the case. Or possibly broke a ring or pinion tooth? It has 3.73 gears and a newer ford racing differential according to the previous owner.

Or is the transmission toast? I kind of felt like I couldn't shift it for a sec. I know it has a leak at the tail shaft. So maybe the input shaft went and the smoke is tranny fluid??

Yeah when I get time (which I rarely have)I will pull the cover. A friend of mine seems to think it may be the input shaft. Just checking to see if anyone has had a similar experience on here.

Update:

Found a little time this evening and pulled the cover on the diff. Everything looks fine, no metal broken anywhere. Everything spins without issue.

Next thing I am going to check is the rear drums. The whole smoke show I had and friction smell makes me wonder if it's brake related. Really scratching my head here guys....any other suggestions or things I may have missed looking at the diff?

The transmission has a tiny leak coming from the tail shaft seal. Not sure if it's just a bad seal or what. It seems to shift fine though.

I will check the backlash. I still have the cover off so I will before I reinstall it. I looked as much as I could at the spider gears and I don't see anything wrong. I will take another look in case though.

Tonight I just took the rear drums off and it's rusted bad in there. The right drum was very hard to get off, had to use my sledge. A bunch of black brake dust fell out on that side and was in the drum. The left side came off without issue although it's rusty in there. I am going to replace everything in there since it almost looks like original parts.

Also a thing to note is when I picked up this car the e brake cable that comes from the lever itself was broken. I replaced that but never thought twice about the rear cables going into the drums. I am wondering if that right side was binding somehow. I believe there is a good chance that this is the problem. I ordered a set of cables just in case. This car has 160,000 miles on the body so these things are bound to go bad sooner or later.

I will update once I rebuild the rear brakes and such. Thanks for the comments and suggestions.

Ok, so I replaced the rear drum brakes and the e brake cables. The e brake works much better. However, I still get the vibration sound. I found that it only happens on decel. If I put it in neutral, the noise goes away. Is this perhaps a transmission or clutch issue?

I did get on it and didn't notice any weird smells. Just burnt rubber and tire smoke...