if you can move the driveshafts universals at all as in up and down or side to side on say the driveshaft end and the end that bolts up to your diff stays still then you have a stuffed uni and they are a easy fix that you can do yourself.
The rotation movement before it bites is the amount of lash or backlash from the point where your gearbox output shaft bites the gears in the gear box to when the pinion bites the crown wheel in your diff, there is always a little movement which is necessary, if you can hear the diff loading and unloading usually with a noticeable clunk when you put your foot on the gas and bring it off again then you have too much slop in your diff and you will have a huge amount of rotation before loading with your driveshaft. (there is no loading or unloading from the axles they are splines not gears)