Would it be worth adding the heavier Z71 springs for towing a 3800 lb trailer/boat combo? I will be upgrading to new Bilstein HD shocks also. It seems to tow the boat just fine, but I may be loading some more gear in the rear of the Envoy adding to the total. Just wondering if the Z71 Springs would be a good upgrade. Or would it make it too stiff for when I'm not towing? Thanks for any input. c good