Everyone's opinion for rear end to go with?

Wallace racing calculator can get you close to the right gear the first time.
for example, if your truck can pull 6500 in the lights,, with a 30" tire at 120 mph, you need a 4.84. So, 4.88s obviously.
For other conditions, wallace will help you out.
(Frankly, 4.88s would have been my choice for your truck, too)