blocks have nothing to do with your spring rate or its flexiblity and articulation. blocks can affect axle rap though. with that said for towing purposes you want your springs to be somewhat stiff or you will have to much sag in the rear of your truck when towing. if you are towing less than 5,000 lbs a block with the stock springs is ideal in my opinion. if you are towing more than 5,000 lbs then add 1 real thick leaf to your stock leaf pack and put in a smaller block to keep your truck level. if you want to have good spring flexibility and articulation for 4 wheeling and still be able to tow then ditch the stock leaf pack and go for a custom offroad multi-leaf pack and install air bags to use for when you are towing loads that weigh more than 5,000 lbs. just know that with custom multi-leaf 4x4 packs they will get out of shape quicker and you will have to get them re-arched sooner than the stock leaf packs.