I am thinking of swapping the stock 3.08's for 3.55's in my '91 rear
end. A friend told be that it's not a good idea because the gears are
normally lapped at the factory and if I replace them, my diff is going to
howl. Can anybody comment on this?

I am also toying with the idea of replacing the carrier assy. with
either a new limited slip or possibly a locker. Is this something the home
mechanic should try or am I better off getting a mechanic to do it? Is it
simply a tedious thing or does it take special tools?