the seat top would only be an inch or 2 above a 5" hump - might wanna check things out closer, don't know why a bigger truck would have a smaller hump, the cab floor is the same distance above the frame, as the engine and trans should be, and the top load trans sticks up much higher than a 3 speed ....
this big 64 GMC looks to have a higher hump than an 'inch or so', maybe yours has been changed?
Bill
