Just got a Yukon, 03, SLT, 1500,5.3 L., 3.73 axle ratio. I haul an open car hauler trailer, 4000 lb. In tow haul mode it shifts down on mild grades at moderate speeds (60-65). I tried it without tow mode and it seemed to pull easier with less engine revving. I let it slow down on inclines. Would this be ok or should I stay with he Tow Haul Mode?