I don't know about your diff going out, but check your u-joints. Make sure there is no play in the driveshaft while you have it parked.
1990 YJ, Colorado Red
with 'Laredo' markings, 4.2L, TF999, NP231, Valvoline Syn fluids, Weber 32/36
, Nutter Bypass, Dana 30/35, 16" Electric Fan, Optima Yellow Top
, 140amp alt., K&N Air Filter, Cherry Bomb muffler, SRC Front Bumper, CH&F Shackles, KC 100w Daylighters, Homemade Lightbar, Rear Aux lights, Cobra CB/PA/WX, 102" Whip Ant., 400 watt power inverter, 2 fire extinguishers, Mobile Internet & WiFi equipped.
Daily Driver since April 23rd, 2003
Northern Illinois Extreme Jeep Club Member www.extremejeepclub.com
Weber 32/36 Install -> http://www.jeepforum.com/forum/f12/weber-32-36-install-write-up-382309/
Early YJ Club Member #37
For anyone with a 4.2L --> http://groups.jeepforum.com/258s_Unite