Problem with my differential ?

Got a problem with the Stang.

I've taken my car tp two mechanics. The mechanic I took the car into recentlly, told me; my clutches in the axles/ differential where going out, he was putting in new breaks on the rear, and noticed the passenger wheel would'nt spin freely like the driver wheel would, he also told me that's the same reason my car hesitates when Hitting the gas pedal on Drive. Mechanic #2 told me my axle bearings where going out.

About 2 years ago while driving my GT in the snow I hit a patch of black ice and my mustang ended up at the bottom of the freeway on-ramp ditch (30 feet deep). One reason why I think I've got a problem, and the fact that when I hit the gas pedal while the car's stopped, the back end will fish tail until there's enough traction (my tires have alot of thread life to them 5/32 I beleive according to midas standards great).
Any ideas ?