I have a 02 screw 5.4L 4x4. Next year a 4" Rancho lift will be going on. I currently have 3.55 gears w/ the factory limited slip diff. I have 285/75/16 BFG A/T's and when those wear out I'll be putting on 315/75/16 BFG's I know I will need lower gears for the 35's and I want to do Detroit lockers front and rear. does this sound good? I do off-road some but nothing really hard core wheeling or rock crawling just mild to some moderate trails is all I want to to.

 

some 4.56 gears would be good, but the detroits are great off road but not so good on the road. some limited slip diffs (alburn) would be better for mild wheeling time to time. or a tru trac from detroit thre are some trac locs also see 4wparts

 

4.10 or 4.56 gears. 4.10s will be probably be more economical, while 4.56 will give you better towing and low end performance.
I don't mind my rear Detroit locker, but a lot of people don't like automatic lockers.

I would not recommend installing an automatic locker in the front differential. With a rear locker you will almost never need a front locker unless you are doing some serious wheeling, and even then it's rare. I had a Sport Trac with Aussie lockers (automatic) front and rear, and the front locker makes the steering a lot tighter in 4x4 and places more stress on the CV joints. In the snow it is very awkward with a front automatic locker. I probably wouldn't run a front automatic locker on again unless it was on a dedicated trail rig with built axles.

If you decide to run a limited slip, I would recommend the true trac over anything else. It is gear driven, won't wear out, and has a higher bias than a clutch based limited slip.