I have a 2000 Excursion 2wd with V10. We recently bought a 21foot toy hauler, the truck pulled it with no problems the first trip out. The issue I have is even with a weight distribution hitch it really sagged the rear end. The trailer loaded down is about 8k pounds. Would you guys recommend heavier rear springs or to add air bags? This is the wife's daily driver so don't want to get to crazy with whatever direction I go.