I have a 1999 250 2 wheel drive, was riding about 40 mph when all of a sudden the rear wheels locked up..any suggestions

 

ide start at the rear wheels and make sure the bearings are ok. rotate the wheels back and forth while looking at the drive line components, like the drive shaft and axle shafts. see whats not turning, you may have to undue the drain plug and check the fluid in the differential. those pinion seals are often neglected the shaft boot gets torn and dirt and water get in there and ruin your day. if all that checks out then yes you have a have a trany issue. i dont know much about the 250 but my 400 4x4 dropped the starter gear and locked the engine up. that was a pain. but start where the problem is and fallow the drivline to the engine/trany. can you still shift it through the gears or is it stuck?