Thanks for pointing out the obvious on that chart Albert. No way to get the 3.55 E-Locker on a 4x4 PowerBoost SuperCrew, so oh well. Now I have to decide how bad I want Pro Trailer Backup Assist, since if I go KR I get the brake controller included. But with no towing specs available, I think I need to pony up for 53C regardless, becasue otherwise I could end up with some lame 7500 lbs trailer limit. Thank you both for the assistance.