If this is what your truck came with stock, the gear ratio numbers on teh door jam should be G254. What size tires are you running now. If ytou are running 30's, I don't think the 4.88's would be too much, since they stock auto's w/31's ran the 4.88's, however if you have 28's or 29's, the 4.88's would be a bit high. I would go ahead and run the e-locker and 4.56's since you already have them and relatively new tires. Before buying 4.88 stock diffs, I would try a set of 33's to see how much diff. there is in power, and wether or not you mind the diff. In the long run, I think the best set-up would be to bump up to 31's as your daily tires w/4.88 diffs, and then run the 32's- 33's for the trail.

Another option would be to swap in a 5-spd and clutch when your current tires are ready to be replaced. This would be a little more labor intensive, but might be cheaper getting the used parts. You would also see about a 4-5mpg increase w/the 5-spd over the auto.