I have been running a True-Trac in my front axle for 6 years. It has performed flawlessly on every surface, including smooth wet granite. The only thing I can say about it is it is picky about the fluid. I change mine once a year (more if I have taken a lot of trips) which is 8,000 to 10,000 miles, and that seems to be enough. I chose it because of price and maintenance ( no air lines to worry about, no compressor, etc.). However, for the rear of a truck I would recommend a selectable locker. I had a Ranger with a Torsen style LS in it and it was down right dangerous in slick conditions. I had to drive with a very light foot.
If you can afford it go with the ARB in the rear. The True-Trac in the front would be fine.
2001 XJ Limited - 4.0, AW4, NP231, HP D30/TruTrac C8.25/Detroit, 5" lift, AJ's Rock Rails, other STUFF.