I have Timbrens on the back, and will probably switch to bags... I'm not happy with the effect the timbrens have on ride unloaded. I'm not concerned about affecting the long term health of the truck, the oil, engine and trans temps are consistently stable, and normal, even in the heat of Calif. Although the 3.55's probably effect the off the line performance, I have no complaint about it, and wouldn't need better.
Keep an eye on the gauges as your towing, drive it like you own it
and it will treat you well.