New at lowering. Question: Which would be better? I would be towing 4000 to 5000 lbs as well.

 

The flip kit will get you lower with out the use of blocks, but will require the addition of a C notch in the frame. Also you can get a good 4 inches of drop from doing hangers and springs.. Blocks don't work on fullsize trucks unless you have done the flip kit to it, due to the axle being under the springs, unlike the s series trucks.. I would do a hanger kit, some drop spindles or springs upfront.. If you do tow with it a set of air helper bags will be the way to go.. Hope that cleared up some stuff