I recently learned that it is relatively easy to lower the back of the truck. Looking under the truck in the vicinity of the rear axles you'll see a block sitting on the axle with the truck body/box sitting on top of the block. That block can be swapped out for a thinner one. That is going to be my first step and then I'll reassess and go from there. The rear of the truck can't be lower than the front or handling characteristics become compromised. Measure from the top of the wheel well to ground both front and rear and compare. I'm pretty sure the back of my truck can be lowered 2 inches. But I'm taking it to a shop that specializes in these type of modifications and get their opinion first.