ps.. don't get crazy on the rear end.. low gears are fine.. but they limit your top end speed, and will make you drink more fuel at high speed.
my 99 450 has a 4.88 rear.. at 72mph i'm turning 2750 rpm.. as you know that engine starts redlineing at about 3300 or 3400.. thus I run synthetic oil.. I once made a hul .. 14k on my gooseneck.. ran 75.. got about 4.5mpg
next tiem I made that haul I dropped to 67-72.. and got 9mpg huge difference.
My 350 has 4.10 gears. much better choice for towing. still decent power.. and ok interstate speed. better power than a 3.73 the other common rear end for them fords..