Sorry for the noob question but what is TSB? I really like what youve done and im looking at getting the 5100 and am still settling on what i want for the rear (putting spindles up front). Truck looks good!
It applies to the rear leaf spring pack in the context we're discussing. The three leaf pack from the factory is/was inferior and caused a lot of drooping of the bed under moderate load. Many people get them upgraded to the improved four leaf spring pack.