[skyhammer]

A detroit locker locks your rear wheels all the time. The e-lock only locks the rear wheels in 4lo. Other than that they operate the same. If had the choice to use the E-lock in all drive modes That would solve my only problem with the E-lock.
If I were you I would not get a detroit locker for the rear of your Titan. You will have difficulty turning on to Berkley's narrow streets. Have you ever tried backing up a travel trailer with a locked rear end? It ain't easy. I have a locking rear end in my 85 Toyota. I only drive it on pavement in a emergency.
As far as putting an ARB in your front diff, I would ask how often you think you would use it. Once you lock yor front wheels steering is going to be tough(especially if you have your rear wheels locked).
Here's my advice: If you don't have E-lock now, I would go with the ARB in the rear. I would leave the front diff. alone unless you want a real rock crawler( which means more mod$ to take advantage of increased traction).