Purchased 2013 F150 Eco boost with super crew and 6.5 ft box. Much to my surprise and disappointment when i put about 700 lbs in my box I got a significant shudder from a dead stop. Ford says this is normal ???? This issue is only with the longer truck not the shorter box. If i had known i wouldn't have purchased this truck. Tech says its an alignment issue of sorts but this is normal. What a lot of crap. Can someone help?