Rear Lockers

To be honest, if you are looking at a rear locker, you shouldn't be looking at 2wd vehicles. But I do understand the dilemma that there are hardly any RVs which with dual rear wheels which are 4wd.

A locker like the detroit is supposed to unlock when turning and lock when you need. They have a reputation of putting people sideways but i think you are okay if you just drive like a sane person should.

The detroit will unlock on turns but only if you don't have power applied. I had a Jeep Scrambler built up on 35s with detroits front and rear. Never had a problem with it putting me sideways but maybe because I didn't have a large powerful engine.

The Eaton True-Trac was my backup choice and a close runner up to the detroit. The best way to think about it is as a torque multiplier. If one wheel is in the air without any traction requiring zero torque to turn it, there will be zero torque applied to the wheel with traction. If one wheel is in slippery conditions and requires 500 ft-lbs to turn it, the other wheel will have 2,500 ft-lbs of torque applied. You can fake the true-trac out by apply the brake to generate required increase of required torque. This assumes a 2.5 multiplication factor which is about what the True-Trac is rated. The nice thing about the true-trac is unless wheel slip occurs, the power is evenly divided to the two wheels so it goes completely unnoticed until needed.

I'm surprised it doesn't come with some sort of posi from the factory. I've had a zexel-torsen which is same type as the eaton tru-track and I like it a lot. I also have the g80 locked from gm the eaton gov-lock which seems to work okay. Honestly I think they all work pretty good provided you drive right even a locker. A locker like the detroit is supposed to unlock when turning and lock when you need. They have a reputation of putting people sideways but i think you are okay if you just drive like a sane person should. We welded my buddy's diff to essensially a full spool and he drove that thing daily wheels chirping on every turn. There is nothing to lock manualy on any of them like an old 4x4. The 2x4 lockers are self contained mechanisms that just work automatically.

Some sort of limited slip will be mandatory, IMHO, on a 4x2 dually. Not enough ground pressure. Most of the weight on an empty pickup is on the front axle. I've used almost every type and each has it's plus and minus. I'm with Kettner with the Detroit Eaton True Trac. Torque biasing means the axle actually delivers traction to the wheel with the most traction, not the other way with an open diff. Since I only wanted it for snow, ice, and sand, I installed one each on the front axle of my Dodge and '99 Jeep not-so-grand Cherokee. They both work exceptionally well in snow, sand, mud and generally poor traction situations. Of course, they both have a rear L.S. also: the truck has a tried and true, Power Lok limited slip,(cone shaped wet clutches are under high preload so don't break away easily) and the '99 XJ has the factory track loc. (aka: trash-lock) They don't last more than 60K miles in normal use. You may think it's working, but it is slowly degrading.
Unfortunately, a 2WD dually is the worst of all platforms on ice and snow, especially with no weight in the bed. Very skinny actual snow tires with lots of siping will help some.
Because we never get our axles twisted up, like hard core jeep-types do, a full locker won't do you much good. This has been hashed over and over on this forum.

I have limited slip on my past Fords and it works pretty well. However, it's not as good as the GM locker. I don't think I'll ever need a locker with a load.

GMs have a locker that works awesome. It will get a little sideways in slick weather but the wheels will turn. This is a pretty good explanation of it. http://www.autoevolution.com/news/a-simple-guide-to-the-g80-locking-differential-94874.html

A locker should not be used on high traction surfaces. It is used only when you need to drive both wheels at the same speed. Limited slip is best option for additional traction on a 2wd if you are worried about slick roads.

Open is all you need on a paved road in dry or wet conditions.
Off pavement or slippery conditions is when you want a locker or limited slip differential. I am partial to Eaton Truetrac if it is available for your differential.

Limited slip is great. Have it on our work trucks. With the weight we carry on the rear axles, it's a life saver in loose material, snow, mud, etc.

I'd be fine with it on a TC..