I agree about the rear sag issue, I hate to see truck higher in the front than in the rear, but my 2" nose down bothers me also, and I don't haul much very often anyways. If it did, I'd probably install air-bags....that way I could run level all of the time.
AS for the WMO...most people on here are running waste motor oil that they get for free with a 15 RUG (regular unlead gas) mix and calling in W85...so they end up with almost no cost in the fuel other than their time spent filtering the oil. It sounds very scare.....but there are a lot of people on here that claim to have been doing it for a couple of years and up to 40,000 miles....with no ill side affects.