[96ImpSS]

How often, or miles per year, do you intend to tow that 6500 lbs?
In flat terrain you can make it work. Take it relatively easy on the throttle on takeoffs, manually hold the gears longer as it's accelerating up to speed, manually downshift before upgrades to give the TCC a chance to re-lock before you really get into the throttle to make the hill, and your powertrain will last a long time.
I'd be most concerned about how stable a regular duty half ton suspension will be with that much load in an emergency situation.
If you must do it, forget the 2 second following rule, use the 10 second rule!