Yea, i'm sure there are numerous variables to consider.. the size of the cab, the length and height of the bed, vehicle speed, cross winds, overall vehicle height, etc.
I know that the fuel mileage hasn't changed any noticeable amount on the '89 K2500 after I trashed the tailgate and been driving around without it.
But that's a full size truck.. it might make more of a difference on 'toy' trucks with lower profile cabs.
But having ridden in the bed of many a truck, both big and small, I can say I never noticed a definitive 'front to back' wind or felt like I was going to be blown out the back.. and regardless of tailgate position, loose papers always seem to blow out the side of the truck when they blow out.. never straight out the back.
