Going to haul the horses to a show and scrolling through menu and notice that the DEF says below 1/2 full. Roll into local ford delaership and buy 21/2 gallon jug and truck only takes 1 gallon?????? Service manager comes out and checks level in the dash and DEF says ok so it is good to go??????. My marth tells me this is a cab chassis and should have a 6 gallon tank so below half shoud have easily taken the 2 1/2 gallon. Truck pulled 16,000 pounds for 7 hours and def stills says ok any ideas???