I have a 2006, TRD Sport, 4X4. I also have the non TSB, 3 leaf, factory springs. The problem is: When I tow a trailer or haul my Polaris (550lbs) in the back of the truck, I have a lot of rear end squat. To make it worse, the truck has a leveling kit on it, so it is even worse than if it didn't have the kit. When I go up in the mountains, I am on the bump stops a LOT! I tried to convince Toyota to give me a free set of TSB springs, but no dice. My truck has too many miles on it and too many years for them to give a frak. I put on some helper springs, but they are a temporary measure. (They were also free!) I would like to either pick up a set of the 4 leaf TSB springs second hand, or replace the springs completely. I know it will change the ride of the truck, but since I actually haul with the truck, I don't care. I am curious what direction I should go, and since there are lots of Taco owners on here, I thought I would ask for some advice. I called Toytotec, and the AAL they have only add about 100lbs to the capability of the truck. Airbags are a definite option, and I have looked into those, but don't have a lot of experience with airbags on a midsize trucks. Opinions would be helpful, links to products would be more helpful, and pics wowuld be great.